Is there a website or mechanism for comparing total costs of two vehicles over their lifespan?

I am in the market for a (new) used car. I have a couple of cars in mind that are roughly the same price, though one will likely cost several thousand more. I am under the impression that one will be significantly more expensive in the long run owing to lower gas mileage and possibly higher expenses. Is there a simple way to get an estimate of future total costs?