HomeSearch by dateVacation packagesHotelsFlight dealsCar rentalTravel tips & news
Pennsylvania

$42+ Cheap flights from North Carolina to Pennsylvania

This is the cheapest one-way flight price found by a Cheapflights user in the last 72 hours by searching for a flight departing on 3/6. Fares are subject to change and may not be available on all flights or dates of travel.
RDU — PHL
Mar 5 — Mar 121
Thu 3/5
Thu 3/12
1 adult, Economy
We work with more than 300 partners to bring you better travel deals

Find cheap flights from North Carolina to Pennsylvania with Cheapflights

1. Tell us where you want to go

Enter your travel information like dates, passengers, trip type (one-way or round trip), and preferred cabin class then click “Find deals”

2. Select your favorite providers

We find the providers serving your travel needs. Choose up to four travel providers to compare side-by-side for flights, hotels, or car rentals.

3. Compare prices and book

Review each provider’s pricing and select the best option for you! Book through your favorite provider’s website for a seamless experience.

Cheap flight deals from North Carolina to Pennsylvania

Cheapest flights from North Carolina to Pennsylvania
Explore the most affordable flight options available from North Carolina to Pennsylvania. Find the lowest fares from popular airlines and budget airlines, with prices last updated on February 3, 2026.

This Travelocity deal was found by Cheapflights users on 2/2. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Travelocity is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 2/176:08 pm
RDU
-
EWR
Nonstop1h 51m
Spirit Airlines
Wed 2/183:30 pm
EWR
-
RDU
Nonstop1h 41m
Spirit Airlines
Deal found 2/2$75
This Kiwi.com deal was found by Cheapflights users on 2/3. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 3/106:08 pm
RDU
-
EWR
Nonstop1h 51m
Spirit Airlines
Sat 3/143:54 pm
EWR
-
RDU
Nonstop1h 35m
Spirit Airlines
Deal found 2/3$76
This Kiwi.com deal was found by Cheapflights users on 2/2. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 3/76:08 pm
RDU
-
EWR
Nonstop1h 51m
Spirit Airlines
Mon 3/93:30 pm
EWR
-
RDU
Nonstop1h 41m
Spirit Airlines
Deal found 2/2$77
This Expedia deal was found by Cheapflights users on 2/1. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Expedia is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 2/113:49 pm
RDU
-
EWR
Nonstop1h 41m
Spirit Airlines
Wed 2/183:30 pm
EWR
-
RDU
Nonstop1h 41m
Spirit Airlines
Deal found 2/1$78
This Expedia deal was found by Cheapflights users on 2/2. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Expedia is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Mon 2/233:12 pm
CLT
-
LGA
Nonstop1h 47m
Multiple Airlines
Sat 2/285:30 pm
LGA
-
CLT
Nonstop2h 19m
Multiple Airlines
Deal found 2/2$78
This CheapOair deal was found by Cheapflights users on 2/2. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure CheapOair is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 3/66:08 pm
RDU
-
EWR
Nonstop1h 51m
Spirit Airlines
Mon 3/163:54 pm
EWR
-
RDU
Nonstop1h 35m
Spirit Airlines
Deal found 2/2$79
This Expedia deal was found by Cheapflights users on 2/2. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Expedia is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 3/63:12 pm
CLT
-
LGA
Nonstop1h 47m
Multiple Airlines
Thu 3/124:30 pm
LGA
-
CLT
Nonstop2h 18m
Multiple Airlines
Deal found 2/2$79
This Priceline deal was found by Cheapflights users on 2/3. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Priceline is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Fri 3/136:25 pm
RDU
-
EWR
Nonstop1h 35m
Spirit Airlines
Tue 3/173:54 pm
EWR
-
RDU
Nonstop1h 35m
Spirit Airlines
Deal found 2/3$80
This Flightnetwork deal was found by Cheapflights users on 2/2. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Flightnetwork is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 2/175:54 pm
CLT
-
LGA
Nonstop1h 55m
Frontier
Sun 2/224:59 pm
LGA
-
CLT
Nonstop2h 18m
Frontier
Deal found 2/2$80
This Kiwi.com deal was found by Cheapflights users on 2/1. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 2/186:08 pm
RDU
-
EWR
Nonstop1h 51m
Spirit Airlines
Thu 2/193:30 pm
EWR
-
RDU
Nonstop1h 41m
Spirit Airlines
Deal found 2/1$81
This Super.com deal was found by Cheapflights users on 2/1. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Super.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 2/145:54 pm
CLT
-
LGA
Nonstop1h 55m
Frontier
Tue 2/174:59 pm
LGA
-
CLT
Nonstop2h 18m
Frontier
Deal found 2/1$81
This Frontier deal was found by Cheapflights users on 2/2. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 2/116:14 pm
RDU
-
LGA
Nonstop1h 35m
Frontier
Mon 2/164:59 pm
LGA
-
RDU
Nonstop1h 53m
Frontier
Deal found 2/2$82

Find flight deals from North Carolina to Pennsylvania

Keep the following information in mind while searching for North Carolina to Pennsylvania flight deals. Data was last updated February 3, 2026.

Most accurate provider

FlightHub
3 stars

Most trusted provider

FlightHub
3 stars

Round-trip from

$75
(Travelocity)

One-way from

$42
(Super.com)

Popular in

November

Cheapest in

February

Average price

$139

Good round-trip deal

$138 or less

Good one-way deal

$94 or less
Provider with most accurate pricing for Raleigh-Durham-Philadelphia flight deals.
Search Deals
Provider most trusted by Cheapflights users for Raleigh-Durham-Philadelphia flights.
Search Deals
From North Carolina to Pennsylvania
Search Deals
One-way flight from North Carolina to Pennsylvania
Search Deals
Highest demand for flights based on searches. 12% potential increase in price ($22 potential increase over avg. RT price).
Search Deals
Cheapest flight prices on average. 2% potential price decrease ($5 potential savings vs. average RT price).
Search Deals
Average for round-trip flights in February 2026
Search Deals
Price to beat on a round-trip flight from North Carolina to Pennsylvania.
Search Deals
Price to beat on a one-way flight from North Carolina to Pennsylvania.
Search Deals

Cheapflights Fare Finder

 
Customize your flight search to find flights from North Carolina to Pennsylvania that fit within your specific budget. Explore options based on user searches and filter the results based on your desired price range. Find flights that match your budget for a cost-effective journey. Over the last 7 days, Cheapflights users made 2,558,603 searches. Data last updated February 3, 2026.
Use the filters below to find and compare flights from North Carolina to Pennsylvania that are best for you.

Fly from

North Carolina

Fly to

Pennsylvania

Route

Depart

Return

Price

CharlotteNewark

CLT - EWR

CLTEWR

Charlotte Douglas

Thu 2/26

1:24 pm-9:09 pm

1 stop7h 45m

Newark

Sat 2/28

10:00 pm-11:59 pm

Nonstop1h 59m

$99

CharlotteNew York

CLT - LGA

CLTLGA

Charlotte Douglas

Sat 4/25

3:16 pm-5:03 pm

Nonstop1h 47m

New York LaGuardia

Sun 4/26

9:55 am-11:59 am

Nonstop2h 04m

$118

CharlotteNew York

CLT - LGA

CLTLGA

Charlotte Douglas

Tue 4/21

3:16 pm-5:03 pm

Nonstop1h 47m

New York LaGuardia

Sun 4/26

9:55 am-11:59 am

Nonstop2h 04m

$118

CharlotteNewark

CLT - EWR

CLTEWR

Charlotte Douglas

Wed 2/18

9:21 am-11:19 am

Nonstop1h 58m

Newark

Thu 2/19

12:02 pm-6:18 pm

1 stop6h 16m

$119

RaleighNew York

RDU - JFK

RDUJFK

Raleigh-Durham

Tue 3/10

5:38 am-11:50 am

1 stop6h 12m

New York John F Kennedy Intl

Tue 3/10

4:15 pm-11:32 pm

1 stop7h 17m

$123

RaleighNew York

RDU - JFK

RDUJFK

Raleigh-Durham

Wed 2/18

6:59 pm-8:59 pm

Nonstop2h 00m

New York John F Kennedy Intl

Sun 2/22

8:15 am-10:11 am

Nonstop1h 56m

$127

RaleighNew York

RDU - JFK

RDUJFK

Raleigh-Durham

Sun 2/15

10:00 am-11:38 am

Nonstop1h 38m

New York John F Kennedy Intl

Sun 2/22

8:15 am-10:11 am

Nonstop1h 56m

$127

CharlotteNewark

CLT - EWR

CLTEWR

Charlotte Douglas

Fri 2/20

9:07 pm-11:05 pm

Nonstop1h 58m

Newark

Sun 2/22

10:00 pm-11:59 pm

Nonstop1h 59m

$128

RaleighNew York

RDU - JFK

RDUJFK

Raleigh-Durham

Thu 2/19

7:07 am-9:00 am

Nonstop1h 53m

New York John F Kennedy Intl

Thu 2/26

12:28 pm-2:19 pm

Nonstop1h 51m

$129

CharlotteNewark

CLT - EWR

CLTEWR

Charlotte Douglas

Thu 2/19

5:55 am-2:54 pm

1 stop8h 59m

Newark

Fri 2/20

12:02 pm-11:56 pm

1 stop11h 54m

$134

Flights are sorted by cheapest round-trip flights first.

Deals found on 2/1

Showing 1-10 of 60 results
1
2
3
...
6

Best time to book a flight from North Carolina to Pennsylvania

Have a flexible travel schedule? Discover the best time to fly to Pennsylvania from North Carolina with our price prediction graph.
Estimated round-trip price
Rates are based on past data. Find the cheapest month and day to book your flight based on your travel requirements, then search for cheap deals.

Cheapflights Insights

Everything you need to know about your flight from North Carolina to Pennsylvania

What is the cheapest month to book a flight from North Carolina to Pennsylvania?

Currently, March is the cheapest month in which you can book a flight from North Carolina to Pennsylvania (average of $46). Flying from North Carolina to Pennsylvania in June is currently the most expensive (average of $92). There are several factors that can impact the price of a flight, so comparing airlines, departure airports and flight times can provide users with more options.

What is the cheapest time of day to fly from NC to PA?

Find hourly flight availability from North Carolina to Pennsylvania. Discover flight options and departure times throughout the day, allowing you to choose a departure time that suits your schedule. Data last updated February 3, 2026.

It’s optimal to fly from North Carolina to Pennsylvania in the morning. By choosing this option you can save up to 38% on the cost of your flight, compared to a flight in the afternoon.

What is the cheapest day to fly from North Carolina to Pennsylvania?

Use this chart to determine the cheapest time to fly round-trip from North Carolina to Pennsylvania. Price data was last updated on January 31, 2026.

Travelers seeking maximum savings on their North Carolina to Pennsylvania flight should consider departing on Thursday at noon when fares are most often at their lowest. Sunday afternoons flights should be avoided if possible as fares are typically the most expensive at this time.

Weekly flight availability from North Carolina to Pennsylvania

Explore weekly flight availability from North Carolina to Pennsylvania. Discover flights operating on different days of the week, giving you the flexibility to choose a travel day that best fits your plans. Compare info to find the most convenient option for your journey. Data last updated February 3, 2026.

The most flights from USNC to USPA are scheduled on a Monday (12 on average). You will have fewer flight options on Saturday, which is when the least amount of flights are scheduled (2 on average).

Reviews of airlines servicing Pennsylvania

Get insights into the airlines that provide service to Pennsylvania. Read reviews, discover amenities, and learn about the overall travel experience offered by airlines. Use this information to make informed decisions when choosing an airline for your flight to Pennsylvania. Reviews last updated February 3, 2026.
Get a feel of what it's like to fly with Breeze Airways, United Airlines, and American Airlines from North Carolina to Pennsylvania by reading reviews from past customers. You can also see how each airline stacks up in terms of entertainment options, comfort, food, crew/service, and boarding process.
Breeze Airways
8.2
Very good
263 reviews

Overall

8.2

Food

6.7

Crew

8.7

Entertainment

6.6

Boarding

8.3

Comfort

8.2

Reviews

1 / 17
2.0
Mediocre

Justine,Jan 2026

RDU - MCO

1/10, I have never experienced the amount of delays, my flight was supposed to board at 8:34pm, we didn’t board until 3:35am from RDU. The staff got rude and very disrespectful when you asked what was going on it was like we didn’t board until something wrong or were pestering them for answers. I was 1 question 1 time, they were not communicating with us at all. So when our plane was now 6+ hrs delayed and nothing was being said to us .. yeah I think we have a right to ask a question. Everything took so long and was such a process; I have never experienced this before and I’m a frequent flyer, breeze makes spirit airlines look like a 100/10 airline.
Breeze Airways
8.2
Very good
263 reviews
Breeze Airways
8.2
Very good
263 reviews

Overall

8.2

Food

6.7

Crew

8.7

Entertainment

6.6

Boarding

8.3

Comfort

8.2

Reviews

1 / 17
2.0
Mediocre

Justine,Jan 2026

RDU - MCO

1/10, I have never experienced the amount of delays, my flight was supposed to board at 8:34pm, we didn’t board until 3:35am from RDU. The staff got rude and very disrespectful when you asked what was going on it was like we didn’t board until something wrong or were pestering them for answers. I was 1 question 1 time, they were not communicating with us at all. So when our plane was now 6+ hrs delayed and nothing was being said to us .. yeah I think we have a right to ask a question. Everything took so long and was such a process; I have never experienced this before and I’m a frequent flyer, breeze makes spirit airlines look like a 100/10 airline.
United Airlines
7.4
Good
9,232 reviews
Breeze Airways
8.2
Very good
263 reviews

Overall

8.2

Food

6.7

Crew

8.7

Entertainment

6.6

Boarding

8.3

Comfort

8.2

Reviews

1 / 17
2.0
Mediocre

Justine,Jan 2026

RDU - MCO

1/10, I have never experienced the amount of delays, my flight was supposed to board at 8:34pm, we didn’t board until 3:35am from RDU. The staff got rude and very disrespectful when you asked what was going on it was like we didn’t board until something wrong or were pestering them for answers. I was 1 question 1 time, they were not communicating with us at all. So when our plane was now 6+ hrs delayed and nothing was being said to us .. yeah I think we have a right to ask a question. Everything took so long and was such a process; I have never experienced this before and I’m a frequent flyer, breeze makes spirit airlines look like a 100/10 airline.
American Airlines
7.2
Good
11,215 reviews
Breeze Airways
8.2
Very good
263 reviews

Overall

8.2

Food

6.7

Crew

8.7

Entertainment

6.6

Boarding

8.3

Comfort

8.2

Reviews

1 / 17
2.0
Mediocre

Justine,Jan 2026

RDU - MCO

1/10, I have never experienced the amount of delays, my flight was supposed to board at 8:34pm, we didn’t board until 3:35am from RDU. The staff got rude and very disrespectful when you asked what was going on it was like we didn’t board until something wrong or were pestering them for answers. I was 1 question 1 time, they were not communicating with us at all. So when our plane was now 6+ hrs delayed and nothing was being said to us .. yeah I think we have a right to ask a question. Everything took so long and was such a process; I have never experienced this before and I’m a frequent flyer, breeze makes spirit airlines look like a 100/10 airline.
Spirit Airlines
6.3
Okay
8,399 reviews
Breeze Airways
8.2
Very good
263 reviews

Overall

8.2

Food

6.7

Crew

8.7

Entertainment

6.6

Boarding

8.3

Comfort

8.2

Reviews

1 / 17
2.0
Mediocre

Justine,Jan 2026

RDU - MCO

1/10, I have never experienced the amount of delays, my flight was supposed to board at 8:34pm, we didn’t board until 3:35am from RDU. The staff got rude and very disrespectful when you asked what was going on it was like we didn’t board until something wrong or were pestering them for answers. I was 1 question 1 time, they were not communicating with us at all. So when our plane was now 6+ hrs delayed and nothing was being said to us .. yeah I think we have a right to ask a question. Everything took so long and was such a process; I have never experienced this before and I’m a frequent flyer, breeze makes spirit airlines look like a 100/10 airline.
Frontier
5.7
Fair
3,052 reviews
Breeze Airways
8.2
Very good
263 reviews

Overall

8.2

Food

6.7

Crew

8.7

Entertainment

6.6

Boarding

8.3

Comfort

8.2

Reviews

1 / 17
2.0
Mediocre

Justine,Jan 2026

RDU - MCO

1/10, I have never experienced the amount of delays, my flight was supposed to board at 8:34pm, we didn’t board until 3:35am from RDU. The staff got rude and very disrespectful when you asked what was going on it was like we didn’t board until something wrong or were pestering them for answers. I was 1 question 1 time, they were not communicating with us at all. So when our plane was now 6+ hrs delayed and nothing was being said to us .. yeah I think we have a right to ask a question. Everything took so long and was such a process; I have never experienced this before and I’m a frequent flyer, breeze makes spirit airlines look like a 100/10 airline.

Related info for your journey

Find useful and relevant information for your journey from North Carolina to Pennsylvania. Access travel guides, tips, and recommendations to enhance your travel experience. Get information about local attractions, weather, transportation options, and more.

  • How popular is this North Carolina to Pennsylvania flight route?

    Flights from North Carolina to Pennsylvania have been viewed 128 times in the past calendar month.

  • How long is the flight from North Carolina to Pennsylvania?

    For as low as $137, Spirit Airlines can have you in Pennsylvania from North Carolina in 1h 39m. There are 416 mi between North Carolina and Pennsylvania. When browsing for deals, the options you’ll see will be for both nonstop flights and flights with stops.

  • What are the cheapest airlines to fly from North Carolina to Pennsylvania one-way?

    For one-way options, check prices for Frontier. According to our data, you can fly for as low as $39. Users have also found prices from $42 and $51 on Spirit Airlines and Breeze Airways, respectively.

  • Can I find deals for flights from North Carolina to Pennsylvania that include hotel bookings?

    Yes. In addition to deals on North Carolina to Pennsylvania flights, Cheapflights offers vacation packages that include both flights and hotel.

  • How can I find direct flights from North Carolina to Pennsylvania?

    After entering your origin and destination, apply the non-stop filter on the search result page to find direct flights from North Carolina to Pennsylvania.

  • Can I find deals for business class flights from North Carolina to Pennsylvania?

    Yes. Cheapflights offers flight deals from North Carolina to Pennsylvania by cabin class. In addition to browsing deals, you can also filter by cabin class on the search results page after making a search.

  • What is the cheapest month to book a flight from North Carolina to Pennsylvania?

    Currently, March is the cheapest month in which you can book a flight from North Carolina to Pennsylvania (average of $46). Flying from North Carolina to Pennsylvania in June is currently the most expensive (average of $92). There are several factors that can impact the price of a flight, so comparing airlines, departure airports and flight times can provide users with more options.

See more FAQs

Browse thousands of different options on Cheapflights for your next trip

Toggle through the tabs below to find thousands of options on Cheapflights for your next trip.

Alternative routes for North Carolina to Pennsylvania

See prices for flight routes from nearby airports that may be better suited for you.
John F Kennedy Intl to Fort Lauderdale flights
San Francisco to John F Kennedy Intl flights
John F Kennedy Intl to Miami flights
Newark to Fort Lauderdale flights
Newark to Miami flights
LaGuardia to Miami flights
San Francisco to Newark flights
LaGuardia to Fort Lauderdale flights
San Francisco to LaGuardia flights
Newark to West Palm Beach flights
John F Kennedy Intl to Orlando flights
John F Kennedy Intl to West Palm Beach flights
John F Kennedy Intl to Los Angeles flights
John F Kennedy Intl to Las Vegas flights
Newark to Las Vegas flights
Dallas/Fort Worth to John F Kennedy Intl flights
O'Hare Intl to Sky Harbor Intl flights
Minneapolis to Sky Harbor Intl flights
Seattle to Sky Harbor Intl flights
Newark to Orlando flights
Seattle to Las Vegas flights
Dulles Intl to Miami flights
Los Angeles to John F Kennedy Intl flights
O'Hare Intl to Las Vegas flights
LaGuardia to Dallas/Fort Worth flights
Boston to Fort Lauderdale flights
John F Kennedy Intl to Dallas/Fort Worth flights
Newark to Tampa flights
Seattle to Los Angeles flights
Reagan-National to Miami flights
Baltimore to Fort Lauderdale flights
John F Kennedy Intl to New Orleans flights
Los Angeles to Seattle flights
Boston to Miami flights
John F Kennedy Intl to Tampa flights
LaGuardia to Orlando flights
LaGuardia to West Palm Beach flights
O'Hare Intl to Dallas/Fort Worth flights
Dallas/Fort Worth to LaGuardia flights
Newark to New Orleans flights
LaGuardia to Tampa flights
John F Kennedy Intl to Sky Harbor Intl flights
John F Kennedy Intl to San Francisco flights
Fort Lauderdale to John F Kennedy Intl flights
San Francisco to Las Vegas flights
Los Angeles to Honolulu flights
Dallas/Fort Worth to Seattle flights
Minneapolis to Orlando flights
O'Hare Intl to Los Angeles flights
Newark to Sky Harbor Intl flights

Top 8 airlines flying from North Carolina to Pennsylvania

Discover the top 8 airlines that operate flights from North Carolina to Pennsylvania. Compare their services, reliability, and customer satisfaction ratings to choose the airline that best suits your travel preferences and needs. Over the last 7 days, Cheapflights users made 2,558,603 searches. Data last updated February 3, 2026.
AirlineCheapestAverageFlexibilityOn-time
FrontierCheapest$54Average$176FlexibilityNo cancel feeOn-time62%
Spirit AirlinesCheapest$73Average$147FlexibilityNo cancel feeOn-time65%
JetBlueCheapest$86Average$209FlexibilityNo cancel feeOn-time62%
Breeze AirwaysCheapest$97Average$157FlexibilityNo cancel feeOn-timeN/A
DeltaCheapest$98Average$298FlexibilityNo cancel feeOn-timeN/A
American AirlinesCheapest$153Average$392FlexibilityNo cancel feeOn-time71%
United AirlinesCheapest$168Average$350FlexibilityNo cancel feeOn-time69%
SouthwestCheapest$179Average$323FlexibilityNo cancel feeOn-time63%

100% Free

Cheapflights is completely free to use, so you can start saving the moment you arrive.

Book with Flexibility

Our users can plan ahead with confidence and find flights with no change fees

Travel Smart

Millions of people come to us for their flight needs every year. We help make travel planning easy by providing useful insights and data-driven graphs that can inform your decisions.
Site
©2026 Cheapflights