Yeah, repair costs are more expensive than for an ordinary car, due mainly to the high cost of BMW parts. However, the 1992-1998 3-Series is extremely popular, as is the 2.5L inline-6 engine in the 325i. This engine is known to be reasonably dependable. If you make sure the specific car has no outstanding flaws, it should be a good purchase if you are prepared to pay a little bit more for whatever maintenance does need to be done. It's also probably a good idea to find a mechanic who is familiar with BMW's.
Good luck.