Whether you class it as a supercar is open to debate, but I ran a couple of Lotus Esprits back when I was young a single, for most of the time as my only vehicle. I did about 50k miles in my V8-GT over 5 years.
A lot of people had told me that it would be financial suicide to do such a thing. To prove them wrong (?! or not!) I captured every cost I incurred on my blog on pistonheads. Take a look here if you're interested:
http://www.pistonheads.com/members/showcar.asp?carId=161 Although on the face of it, it's a lot of money, I don't regret any of it and i doubt that it is any more (in fact probably less) than I would have spent had i gone for another marque that has less of a reputation for unreliability! Ie it's not just a lotus thing..
The old adage is true: "if you couldn't afford it new, you won't be able to afford it used" :)
Believe me, your mpg is the last thing you need to worry about..
Can't post this without a pic obviously.. :