Popular Mechanics did a cost analysis of the Prius, Plug-in Prius, Tesla and Volt. After all was said and done the Volt beat the Prius on a 200 mile trip by .03 a gallon! The difference between the $22,000 Prius and the nearly $30,000 (projected price) Volt was nearly zip! However, the 40 mile trip is where the the Volt beat the Prius. Same story for the Plug-in Prius. It only shined on short trips when it ran on electricity only. However, the price to upgrade a Prius to plug-in capability was $10,000! That's quite a lot to save a few cents at the pump. In reality, the standard Prius came out as the savings champ of the three when price was taken into account. The only way the plug-in Prius and Volt are better deals is if someone GAVE you one!
As for the Tesla, it cost the least to drive except for the $98,000 price tag!
So, if you want to save money at the pump, buy a Prius and move on. Unless the Volt is priced aggressively its not going to be the success it deserves.
Another promising vehicle is the Air Car. It runs on highly compressed air and has a 200 mile range. It takes only 3 minutes to refill and has a zero pollution factor. Price for the car? They are talking of $18,000! It has a top speed of 98 mph and very nearly zero maintenance (an oil change once every 50,000 as a matter of fact).