Keep in mind that the fuel savings may not be all that substantial depending on where you live and what gas prices do.
Currently our S is running an average of 325Whr/mile, which works out to an equivalent cost of 39mpg where I live. Keeping in mind the size of the S thats still pretty good, but even if the 3 is significantly lower, its quite possible that it won't be significantly cheaper to fuel than a good hybrid ICE.
Course gas prices could also sky-rocket.
Wow, man! How much are you paying for gas and power? I see you live in New Jersey, but I didn't think it was that bad.
I assumed 325Whr/mi for a MS, 30MPG for a comparable full-sized sedan (a number chosen after a cursory look at average numbers), $2.10/gal for gas (about the average in the Houston area), and $0.07145/kWh for home electricity (my contract price if I spread the fixed portion of the delivery charge over 1000kWh). With those assumptions, I get about 88MPGe.
Tesla estimates an average of 333WHr/mile. At the national average of $0.12 / kWh, you pay 3 cents per mile (90D). In a 30MPG @ $2.10/gal situation, you're paying 7 cents per mile.