See Clark's Garage Shop Manual to see a laundry list.
http://www.clarks-garage.com/ also
http://www.clarks-garage.com/purchase.htm
Things like heater clips are cheap, easy to DIY, as is the sunroof gears. The major required expense items are the belts and rollers and water pump. Given the age of the vehicle vacuum hoses can need replacement due to age. I tend to agree with Ski. Unlike Audi A8's that routinely have tranny failures, and BMW V8s that blow radiators every 50k, I'm not aware of any such major problems on the Porsche. It usually tends to be little things due to age and/or neglect. Fixing an oil pan leak can be labor intensive however. Major problems are due to abuse or mods. If I'm wrong correct me please.

 

By the best, newest car you can find and afford. The tune up parts you mentioned are not expensive and easily done at home. For the milage and condition of the paint and the year I think 9K is high. If you love the car offer him $5,500-6,500. You are at a point where some serious maintenace will be needed. You may be looking at a clutch, rotors, gaskets for the head and cam covers as they just fall apart from age, various tubing, h20 pump, fixing power steering leaks. A complete service history is a must on these car and I would suggest a PPI from a knowlegable shop. Do you read Excellance. They give the best market valuations for P-cars. If you are not educated about these vehicles, take someone with you who is familar with them. They are great cars if you get a good one.

 

I have an '87 951 and a '92 968. They seem to require about the same amount ($) of maintenance each year. Do what you can, yourself. There is a ton of invalueable information that can keep you from having to invent the wheel each time something new comes up. I try to stagger major repair/maintenance costs so that I average about $1,500 or so a year per car. That seems to be working for me. I may do timing belts one year, a clutch the next, and tires and brakes the following, for example.

 

I agree with most of what's being said but I still think it's a poor choice for a daily driver for someone who isn't mechanically inclined. Just get a Cayman