The discussion is mileage, which by default brings in carbon footprint.First of all, you may want to have the safety discussion with Floyd. On cost, the Pinto at $700 will win every day, as long as it runs. Carbon footprint, the Prius would kill it.
No way the Prius wins on Carbon footprint. You forgot to calculate, as do most folks, the carbon footprint of making the Prius and the environmental impact of building the battery pack and charging the battery pack...
The Prius Carbon Footprint Myth