Reliability of older (1997-2003) BMW's?

I’m looking into an older BMW to replace my current vehicle. I’m surprised at the low prices of BMW’s in the ‘97—‘03 range. I want a reliable car, my current car is anything but. I’m looking at either a 3 or 5 series, depending on price and mileage.

Has anyone had an older BMW? How did it run? How often did something go wrong with it? How much were parts when something broke? I do my own car maintenance, so I just need to know that the cost of parts is not too exorbitant.