The car has been reliable in general. When acquired, I had the fuel injectors cleaned as this can be a problem on 3.1L GMs. $100.
Spark plug & wires changed, included general tuneup, $100.
That is all for expenses.
The car runs well, never fails to start unless the PassKey II system malfunctions. The car is fairly agile, although there is some body roll and oversteer when you drive it hard. However, for most "normal" driving habits, this car is excellent. Fairly quick to accelerate with the 3.1, good with highway passing.
I cannot stand piston slap however, so I will never buy another GM product again. It was not just this car, it's the fact that since 1999, most of their engines through 2004 and maybe 2005 had it, and had it bad. When it takes a major corporation with sales as high as they have SIX years to fix a problem such as this, it completely turns me off to them. Visit www.pistonslap.com for more information on the issue.
Other than that, if you can see past irritating noises and the chance that your car may lose power (compression) over time, this is a great car to buy used. If you can get a 1995 or 1996 model, those were probably the greatest. 1997 and 1998 models didn't have great reliability, and after 1999 the infamous slap became very apparent.