I wouldn't buy a used M3 with a supercharger. I would want to install it on my watch, and I'm the guy driving it after install. Like others have said, you don't know what kind of wear and tear you are getting into....let's keep it real, you know how we are
I would be afraid of big expenses coming your way...huge gamble.
Besides price is dependent on so many variables....and then layer on your local market demand for pre-owned m3s, and etc.