Wayne, I would try the "gas prices" websites and choose large towns along the route. For example:

www.phoenixgasprices.com

or

www.elpasogasprices.com

are two that I use when travelling from Phoenix to Texas.

Ususally the Sams's Clubs and Costcos have the best prices in our area.

Good luck !!! (Phoenix Average is 2.077 today)