It’s generally more expensive to depart on a Thursday, if you have to leave on this day you can still search on Cheapflights to find great options that meet your needs.
Due to multiple factors, expect to potentially pay more when booking in December. For low rates, October can be a great choice for travel to Casper. Flights to Casper from Missoula in October are about $323 on average during October, but can be found for as low as $245.
It’s typically best to fly out from Missoula to Casper at noon. Doing so could potentially save you 21% on the flight price compared to flying in the morning, which is usually more expensive.