I think you need to grow that sum a lot larger before you think about buying a Porsche of any kind, let alone a Turbo. I'll just start off by saying that any 951 you can buy for as little as $4000 is going to be a complete project car and unless you can do all the work yourself, will cost thousands more to bring around to a decent condition. I'm not sure where you are, by in the midwest a solid well looked after 951 will run $8000-12,0000, with the TLC needing cars fetching about half that.
They're great cars when they are looked after, but too often people can afford to buy them but forget it's still an exotic and still costs like one to maintain. The initial purchase price is only the start of the money you'll put into a Porsche, so if just buying the car is going to leave you high and dry, you need to save more money or maybe think about another car.
The best advice I can tell you is to look for a nice early 944 N/A in your price range, but even then expect to pay a few thousand in maintenance/repairs right away. You're correct about the belts, and if you buy a car with unknown belt history plan to spend about $2000 right away to get that (t-belt, water pump, balance shaft belts, rollers, pulleys, idlers, etc) because if any of those fail, 8 valves x $100 each = $$$.
Very few if any VW/Audi parts can be used on the 944. Parts prices aren't terrible (unless your used to domestics) but it's the cost of labor that really brings the bill up. For example, the front end service (t-belt, water pump) takes about 15 hours, 20 hours for a clutch, you get the picture.
I'm not trying to put you off buying a 944, but I just want your first experience with the marque to be a good one. they're great fun and very reliable if well looked after, but the problem is that there are so many rattle traps or piles of junk that will just turn into a money pit, so you have to know what your getting yourself into ahead of time. Understand it's going to be a real labor of love, expect to spend about $2000 a year to keep her running the way she should, have a shop who knows Porsches check the car out before you buy it so you'll know exactly what you're getting, and I can't stress enough to have a few thousand in addition to the purchasing price of the car saved up for repairs right off the bat. Trust me, you'll need it. Good luck and I hope this helps. BTW- There are tons of 944 buying tips all over the internet, I believe pelicanparts.com has a pretty in-depth guide which would be a good place to start.