its easier just to figure out how many miles your driving, divide that by MPG, and multiply that by an average cost per gallon.
For instance-
3000 miles, / 20.5 mpg = 147 gallons X 1.90 (average price) on the east coast...280.00
One thing to remember, it's not always best to buy elcheapo gas... My truck, for instance, gets much better gas mileage on 89 octane than it does on 87, and runs a whole lot better.
DH's diesel for instance, we have to be very picky with...we only buy at truck stops where lots of big rigs are filling up when on vacation
Brandy