Calculate gasoline savings to amortize hybrid cost?

Hi Dave! I saw your great review of the Toyota RAV4 Hybrid over on your other blog [see Is the RAV4 Hybrid my next car?] and one line caught my eye when you were talking about the surcharge for the hybrid engine: “you can do the math too: at $2.50/gal that’s a lot of driving to pay back the difference”. So how DO you calculate how many miles you need to drive to amortize the cost of the hybrid.

http://bit.ly/1rOMfXb