I own a prius as we have a congestion charging system in central london and the prius is excempt. Petrol here costs £3.80 per gallon, thats at least $7.50 per gallon. congestion charge at £8.00 per day or $15 per day ... call it £1800 per year or $3500..

petrol savings at 200 gallons £450 or $900 ...

so conservatively I reckon I'm just about ahead of the game....

It's not green but my pockets happier....