You will probably be surprised to find that your per-mile costs to fuel cars are cheaper with electric cars than with gas cars. Calculating your per-mile cost for gas cars is pretty simple, as long as you know your average cost for a gallon of gasoline, your typical fuel economy and the number of miles you drive. For example, if your car gets 25 mpg and gas is $4 per gallon, it will cost you 16 cents per mile in gasoline.