Need Advice for buying M3

Here's my deal
I'm trying to save up to get an M3. Hopefully I'm just going to pay cash for like a 1998-2000ish M3 for somewhere in the 13-16k range.

now I'm trying to figure out what I can expect in terms of how many miles i'm going to get out of it--does anyone have any answer to this or any other advice?

it'll be the first car I ever buy so help is greatly appreciated