Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Greensboro to Sioux City as you normally would.
Greensboro/H. Point Airport is GSO and Sioux City Sioux Gateway Airport is SUX. These codes are created by the International Air Transport Association (IATA) and airlines use them to identify the departing and arrival airports in the flight routes they service.