Cheapest way I have found and granted I am in Lethbridge but easily has to be Great Falls on Allegient Air! Not uncommon to find flights direct for between 50-80 a way! Last trip I booked my room separate and used
www.smartervegas.com, just sign up for free and you get access to some hotel promos and can book cheap rooms! Mon-Fri is the cheaper option as said previously, my last trip total for flights and hotel was $420, not to shabby if you ask me!