Same with all 86-87 turbo Buick Regals (GNX, GN, Turbo T, Limited). Low mileage cars are going in the same range. Even complete rust buckets are going for $10k. The hot air 84-85 cars are slowly catching up, but only super low mileage GNs. You can still get a running, driving, decent body 84-85 T-Type that needs work for under $10k and pick up a roller for around $6k. All the people putting LS motors in them is also driving up the price of original turbo 6 cars.
We had a 2002 Regal GS. I had some bolt on performance parts on it; supercharger pully, injectors,
cold air intake, fuel pump, convertor, computer reprogramed. It surprised the heck out of Camaros and Mustangs. The issue I had was I couldn't keep a transmission in it. Kept dropping overdrive after 60k or so miles, even in fully built transmissions (cannot remember which vendor built 2 of them).