Drag Time released a very cool study on how much it costs to race a Model S:
There is also a video (first on the page) showing the regen from 114mph back to 0. It's quite impressive to watch it like that. Ordinarily I never get to stare at the speedometer when driving at 114mph .
PS: I tried figuring out how much a performance gas car would cost for the same run, and the only reference I could find said something about 4 runs per 1.5 gallons. (So $1.50 per run). Anybody have some better numbers?