Body rust is probably the biggest issue. Thats a lot of miles too. Get the engine checked out.
Most everything is available, but $3000 sounds like a lot for this car. I mean there are E36s that are going for that and unlike 2002s , the E21s have never been considered collectable. I mean I owned one for a pretty long time and I like them, but also realistic. For $3000 the car had better be immaculate.