I kind of feel guilty for replying but since the post is still open I will give the crazyjay his answer.
First of all, the 993 been the last aircooled and all so its popular , they dont make them anymore, so the values are holding well.
I own 2 of them. One has 44000 miles and the other one before I swapped for a 3.8 L engine had 83000. The 83000 mile one happens to be my race car so you can imagine the type of miles it racked on
At a race in Putnam , I run the car with a friend of mine on back to back races and sessions. We are talking about at least 5 racing hours per day for 3 days. The 83000 mile engine consumed a tiny bit of the Mobil 1 and kept on running like a champ. I went through 2 sets of Pagid racing pads, a set of brake disks, a set of Michellin Pilot Sport Cups just to give you an idea of what type of wear we are talking about...
In short the 993 engines are bulletproof and a high mile car should not be a worry for anyone. I know of a 993 with 250000 miles and the engine is still original and never rebuilt.
When you find the car you like make sure you get a PPI , a leakdown and compression test and insure that it has full records. You should see OIL change records and OIL is the engine lifeblood.
Like I said in general the 993's are bulletproof but like anycar have wear and tear. Between 70-100K there have been noted to have to change the clutch ( about 2K), brake disks ( which are cheap) , engine seals ( cheap) . spark plugs, belts etc. You should also check the half shafts and the front tie rods. The upside of having a high miles car is that most likely the expensive wear and tear items like the clutch have already been done. In either case you should budget a good 4-5K to bring the car if necessary to absolute perfect health. A couple of nagging issues:
1. There was a recall on the wiring harness from Porsche. Make SURE that this has been changed to the new type. You can veify that by the harness number at a dealer. If not the recall is still open , make sure you do change it!!!
2. On US 96-98 993's due to the emissions regs the OBDII puts out a check engine light due to the secondary airbypass tubes been carbon clogged. Its a nagging thing more than a problem really. If you buy a 1995 it does not have that nagging problem. As a matter of fact I truly believe that a 95 is a much better value because it can be had cheaper and the performance difference in negligable. Further more a 95 can be chipped much easier and much cheaper than a 96 on as the 95 has the older OBDI ECU.
Go buy the one you like and drive it like you stole it! They love been driven hard!!!