Howyadoin,
Well, if my experience is any indication, the motors last. With one condition; '93-'95 Sevilles will not last long if the coolant is not replaced every 2 years or 20,000 miles. Head problems, coolant leaks, etc. can result. '96 and up use Dexcool, so the interval is 100,000 miles.
I kept up with the maintenance on my '93 STS, and it was an absolute blast. Quickest sedan I've ever driven, that's for sure... The launches were a thing of beauty, the car scratching for grip as the front end comes up, a little torque steer but nothing you can't handle. My car had custom exhaust, so it sounded completely evil... (By "custom exhaust" I mean the baffles blew out of the muffler

). Handled well with z-rated rubber, got it up to 130 before the radar detector went off... Top end is 155 with z rubber from the factory, the sticker on the door will tell you. Other than those cars, they're 130 limited. IIRC.
So to make a long story short, as long as the car has had coolant maintenance, hasn't have overheating issues in the past, it's a good candidate for 200K. My '93 was at 150K and was ready to go 200 before I had an accident. I had to replace shift solenoids in my transmission, not an expensive job really. The only other stuff I did was belts, hoses, plugs, battery, oil changes, brakes and tires. That was over the course of 3 years and 70K (Bought it used with 80K). At the time I lost the car, I was getting ready to do a new rear taillight ($200 rebuilt), struts ($500) and alternator ($200). At 150K, that's not too bad, except the taillight, the cost of that one annoys me...
Looking at the prices on a couple websites, $7000 looks reasonable, mileage is below average. Any problems that you're aware of?
I got my '96 SLS with 120K for $3800, but I've had to put a little money into it. A/C compressor is on the way, replaced the blower motor, total of $300 in parts, and it has some scratches in the paint that need to be buffed out when the weather gets warmer, but the car was an absolute steal at $3800. I've put about 5K on it, and it feels ready for another 75.
-Rav