If you don't mind changing planes, you may want to consider flying to Missoula (MSO), Missoula US via Minneapolis, Denver, Cincinnati on Delta and United.
Go ahead and book your flight to Missoula NOW!
In order to get the lowest available airfare, book your flight to Missoula as early as possible, since the cheapest seats are booked months before departure. If you are flexible depart on the first Tuesday of the month, as there are usually some great deals and discount airline tickets on offer.