Here is a site I use to track gas prices. It can some times be off by +$0.10 but is close..
http://www.detroitgasprices.com/Price_By_County.aspx?z=0&lat=37.000000&long=-96.000000
http://www.detroitgasprices.com/Price_By_County.aspx?z=0&lat=37.000000&long=-96.000000