I’ve also read about this before. I found a concept Prius plug-in online that is supposed to get 125 mpg. There’s a company in California that is going to start doing the conversions – it also claims over 100mpg for the converted Prius+.

Taking a look at my hybrid article, given this increase in gas mileage, the ~110mpg converted Prius would need to be cheaper than $14,800 to save you more money than the leading economy car, assuming gas prices stay at about $2.50. If they go up to $3.00, it would need to be cheaper than about $15,200. Dang, that graph is handy.