Wrong call on this one. Gas is the same price or cheaper in places where you have to pump it yourself. Look at the price of non-self serve gas in other states, talk about a rip off!
The variance in gasoline prices throughout the states is really a function of the difference in state gasoline taxes. Look at
this page and you can see that if you live a little north of the Georgia/North Carolina border it is really worth it to drive over to Georgia to fill up. Likewise if you are headed south on US441 hang on until you get south of the border.
Just giving a quick glance at the table, it appears the GA/NC border has the biggest tax differential.