I actually have been dabbling with the idea of getting an 87 GN. It will be a while before I get one because I haven't had a substantial paycheck for 3 months due to changing jobs but I just sold my E36 M3. I just have started researching and getting a good grasp of what these puppies are selling for.
Here are some of the "local" cars I have found online. I've seen some other nice buicks but have decided to narrow it down to an 87 GN bc I like the all black. I like the regal Turbo Ts but I've only purchased black cars and plan on keeping it that way despite loving the way white or blue paint looks on cars.
Weatherford with T Tops(hopefully garage kept) $12k
1987 Buick Grand National 52K Original Miles
Sherman with salvage title and incorrect mileage listed $9900 from a dealer
1987 Buick Grand National
From doing a little dabbling around I think it is this same car I found listed on craigslist Houston for $8k because the description listed roughly the same mileage as the carfax and listed as a salvage title and recovery. There was a listed change of ownership on the paperwork a little before Christmas on the Sherman car's carfax, from Katy, TX. The ad is not up anymore as of today which stinks because I would have gotten the contact info of the previous owner.
My only issue I may run into when I pull the trigger is getting a pre-purchase inspection by someone who knows these cars really well and can get it on a lift and look for specific items a little better than I can with just reading a checklist online. I know how to run a compression test etc. but due to lack of experience with any GN's I am afraid to judge a car alone. Plus the knowledgeable can get a better grasp of what the car is worth than I can!!