I think about $4000 if it is really great condition. You'll have to figure on an engine rebuild (maybe???) within 60K, and that's not cheap. Still you have a great parts car, and should be aboe to keep it running for years.
I'm currently the owner of an '87 535is w/ 272k on it (still runs and looks GREAT), but I've got some hidden rot on the innner/outer rockers, rear quarters, spare tire section of trunk, and pretty much all 4 doors. I'm told it's gonna' cost a small fortune to remedy (and my last name ain't 'Rockefella'), so as a Plan "B" I'm looking at a '87 535i with 240k on it. Immaculate inside/outside (still running those damn TRX's though) and was wondering what's a decent price to offer the guy. I got my '87 from a friend for a song, so I've got nothing to go on experience-wise. Any suggestions would be much appreciated! Thanks- Tim