IMHO, a 50-70k mile, nice condition W02 "87 Turbo T, should be in the $15,500 - $17,500 range realistically. Especially if it was well taken care of, was as close to original as possible and had some documentation. "86-"87 GN's in similar condition should be in the $18,500 - $20,500 range but they're not. They're much higher. The $20 - $25k range should be for the almost 100% original, low mileage cars.
That car listed above has some red flags to me. Let me explain.
A real 20k original mile Turbo Buick, should not need a repaint, unless the owner just couldn't stand the factory orange peel or the car was in a fender bender and needed a repaint. If it was kept in a non conditioned environment, yes the fillers would naturally degrade, start to sag and develop cracks, eventually crumbling and or breaking at the slightest brush of the water hose. I have never seen a low mileage car (to me low mileage is 20k and under) that had a radiator overflow bottle that looked like it came off of a 120k mile car. Every low mileage car I've ever seen, that bottle still looked like new. Most 20k mile and under cars look spotless underneath with the obvious surface rust areas, namely the exhaust and mild steel brackets, etc, etc. Most 20k mile and under cars still have the stock intercooler hoses and air box assembly, unless one of the owners hot rodded it a bit. And most low mileage cars, still have the original plug wires. These are all little details that jump out at me and cause me to question it's history. Don't get me wrong, I'm not trying to down that one in particular, as it is a very nice looking "87 T. My last one, "Sarah", was it's twin, sans the T-Tops. But something about it just seems a little off to me. I say these things because I have personally seen a lot of very low mileage TB's over the years. I have also seen many shady car dealers try to pull a fast one, with an obviously beat to death example, trying to sell it as 100% original. I'm sure there's reasons for all of those little things on that particular car, but I can tell you this, if I had money in hand and was looking at an under 30k mile car that was priced higher that the Weather Channel's satellite, I and my friends would go over it with a very fine tooth comb.
In today's market, you must be wary of the "Used Car" business that's trying to cash in on the crazy rise in Turbo Buick prices. It's not that difficult to take a 120k mile car, clean it up, repaint it, dress it up with new OEM replacement parts and try to pass it off as a much lower mile car at a ridiculous price. Get someone who's been into these cars and knows what too look for to take a very close look at it for you. True brothers and sisters in the Turbo Buick community will gladly help out in that regard, as none of us want to see a new owner get messed over with a lemon.
Unfortunately, the regular Turbo Regals just don't bring the money that the GN's do. I personally feel that it mainly has to do with public perception / memory. Everyone that's into cars, has heard of a Grand National at some point. Very few know about non Grand Nationals. It's been this way since they were new. Even the insurance companies played favorites back then. If you are in the market for your first Turbo Buick, one of the best pieces of advice I can give you is this.
Buy this book ASAP and read up. It is one of the best resources in print that have ever been made about these cars. Even though it came out back in the late 90's, the info it contains is priceless information.
https://www.kirbanperformance.com/product/335/KIRBAN'S+GUIDE+TO+1986+and+1987+BUICK+TURBO+REGALS+BOOK+#6757.html
Unfortunately, Dennis' other book, Kirban's Guide to Buying a used Buick Turbo Regal is long out of print and pretty expensive. But it also has a ton of useful info when buying.
https://www.amazon.com/Kirbans-Guide-Buying-Buick-Turbo/dp/0965844714/ref=sr_1_4?ie=UTF8&qid=1528861036&sr=8-4&keywords=kirban's+guide
Hope some of this helps, sorry to be so long winded and good luck with your search.
-Patrick-
