I think that the term "poor's man supercar" .. is really easy to understand
if you want to buy a supercar, but you can't afford it ... you might be considered poor for that matter .. therefore "poor's man supercar" is really not that hard to think of and I would agree with GTR, Z06, R8 easily considered those
however not the M3 .. M3 biggest problem for me to call it supercar is that there is just way to many of them ... if you own a supercar, you should met 3 or more every time you hit the road.
Also the supercar should have somewhat more sleek body .. .
I don't consider P911 supercar ... supercars are things like Lambo, Ferrari