You should compare it to something that's near its performance class, since people are obviously not going to buy the Model S just to save money. That's going to be a future model.
At under 5 seconds 0-60, the Model S sport is supposedly going to have performance in the 500 horsepower BMW M5 range, which gets a combined MPG of 13 (11 city, 17 highway).
If you are driving that much, you will wear out the batteries even faster than the norm causing the battery cost to be even higher.
Alternately, it's cheaper to drive a fuel-efficient gasoline car like a Volkswagon Jetta until gasoline gets up to $27/gallon.