325is Purchase

I'm looking to buy a 1987 325is. It has 160k miles on it, and it appears to be in good shape. The guy selling it is only asking 3,000, so it seems like a pretty good deal to me. Here is the problem: I only work part time and won't be able to put a lot of money into the car if the engine falls apart. Do these cars typically hold up pretty well in the high milage, or will I have to be spending a few hundred every month to keep it running well?
One more thing: The guy I'm buying it from (maybe) is unsure if it is a 325is or a 325es. He thinks it's an IS, but doesn't know. The badges on the back are gone. Is there a good way to tell the difference? The car I'm looking at has an onboard computer, race seats, and power everything. Is this typical of both the is and the es?
Thank you for your help.

The 325es has a different engine, that's the major difference that I know of. It was only manufactured until 1987, and then replaced by the 325is during the same model year.

You might check the VIN sticker.