Here's a link that ElkHunter left for us on the Wyoming thread. I thought I'd share it with those of you who are looking at posts about Montana. Put in your zip code or zip code for any town and find out the various prices for gas in that town.
Gas Prices - MSN Autos
Also, I wanted to let those of you who are coming to or through Billings to be sure to check out gas prices at various stations. There is one off the King Ave/City Center exit that ALWAYS has prices WAY HIGHER than anyone else in town. It is the only station right off that exit so I guess the owner feels he can charge what he wants and travelers would be none the wiser. There are other stations closeby....just go the other direction off the interstate toward King and you'll find them. Just a helpful hint!