Probably around 5-6K for a decent one. The trans is always a weak link in these cars. Make sure to drive it for a while to get it hot and see how it shifts. Check for trans service records. Engines should be bulletproof as long as they haven't been beat on or modded without other supporting mods (i.e.- smaller supercharger pulley without other mods to go with it). Check for rust in the rear rockers and rear strut towers in the trunk (may have to pull back the carpet to see the top of the towers).
Yes, you should change the S/C oil, but can't remember how often. Get the oil from a GM dealer. Wear gloves if you change it because it stinks and if you get it on your skin you will reek for a week.
Check for any worn out suspension components, leaks from the rack. They don't handle very well, but can be improved. They are decent DD's and can be modified to be more "fun" depending on the wallet. Being the newer supercharged version means you have the Gen V blower so it's a good start over the older Gen III.
You can take a good read through this thread--> http://www.grandprixforums.net/threa...00-Powered-Car!! to see all the things you can do to the car. It's a good start to understanding what you can change and why.
