I hate to say it but 1/2 the price a equal shape 86/87 would be
So if he wants 10 for it would it be worth 20 if it was a 86/87 Just like all cars its worth what somebody will pay and were the car is located. Some parts of the US the cars are worth more than others. What upgrades does the car have and when it was painted did they strip it and do a proper job on the prep work? Did they do a nice job on the door jams,trunk jams and around the 1/4 glass? Or did they mask off that stuff and get primer all over and paint on the rubber. A nice paint jobs alone can be at least $7500 but on the wrong car you wont get your money back.
I would recommend to be patient and keep searching for an 86 or 87 GN or T-TYPE. You will be happier if you're seeking to modify for great street/track performance or keep stock.