Question about a '94 Mkiv TT

I am looking at purchasing a 1994 Supra TT. It has 90,000 miles on it and has the gold package with the TRD clutch, flow through exhaust, and ram air intake. He is asking $20,000 for it. I am wondering if it is a bad idea to buy a car with twin turbos that have 90,000 miles on it. I would be disappointed if they had to be replaced in 6 months. Also, the Kelly Blue Book Value of that car is $14,810 plus the gold package and TRD options. I estimate the new cost of those to be an extra $2000, making it "worth" $16500 to kbb. Is that car really going to sell for $3500 more than the kbb price? My parents are buying me this car for graduation and certainly won't pay more than $100 over kbb. My question is basically how much the market right now will pay for that car, and if kbb means anything to people selling this car. I also want to know if I do buy this car, can I get an aftermarket warranty to cover the engine parts that are working fine now?

Any information helps

Thanks

1994 Toyota Supra TT
Twin Turbo, Targa Top, 6 Speed Manual, TRD Options (Competition Clutch, Ram Air Intake, Flow Through Exhaust), Chrome Wheels, Rear Wing, CD And Enhanced Radio With Rear Center Woofer, 325 Rear Wheel HP, New Tires, Custom Gold Package.