Fuel efficiency on the 392 might not compare to a Prius, but I'd assume that if I have a $70k to spend on a car my job pays well enough for me to afford gas. It probably gets 1-2 less miles than an M3, so it's not far off.
If that doesn't help my argument than hands down an STi. More than enough money left over for gas and maintenance. Not to mention this was what I was considering before the BMW in my garage. /shrug