Ouch. Not much in that price range.
I'll post anything I see...but might I suggest an older 325e 5-speed instead? Don't get me wrong...I love your idea...but you're likely to get a car with a dying motor and shot suspension. You'll end up spending far more money just to keep it on life support.
Don't let the M20 eta motor fool you...it's nearly as cheap to run, motor is far more durable (timing belt excluded), and you can swap an M42 when you're ready. The handling is 95% as good, even with the longer, heavier engine.
The 1988 "super" eta is the one to have, but the earlier ones are nearly as good. Make sure it's a 5-speed, should be good for 250K miles or so.