i get offers for e30 and e36 m3’s as trades all the time, I won’t get rid of it for anything. maybe for 25k i would lol
as far as mileage; e36’s have an m50 (325i/is) or an m52 (328i/is). they have a timing chain, so they’re not as fragile as the e30 325i/is motor (m20, which has a belt, that snaps at 60-70 guaranteed)
i would have no problem buying a 140k e36 if it had been well maintained. but with your budget, you can probably get one with 60-70k, which is obviously better.