NEW YORK (TheStreet) -- Let's say you are about to buy a new car. Let's further say one of your top criteria is fuel economy. Chances are the ever-present Toyota Prius is high up on your list. It's on its third generation and has been in the market for a decade. Customers love it. Millions have been sold.How much will you be paying for gasoline if you buy a Toyota Prius?Let's say you drive an American-average of 12,000 miles per year at the Prius efficiency of 50 MPG. Then you will consume 240 gallon per year. At $4 per gallon for gasoline, that's $960 per year.