You can have a look at a recent thread for a similar car...
http://www.turbobuick.com/forums/threads/5k-mile-86-worth.424059/
Depends on a few things as mentioned:
- Are you the original owner?
- Do you have complete service records dating back to the car's delivery?
- Have those 3,000 miles been put on in a manner appropriate for the maintenance of the car?
- Has it been stored properly?
- What other options does it have?
- Location of the car.
There are other considerations as well. T-top cars don't generally bring as much as hard top or astro roof cars, for instance. Still, the car is probably worth somewhere in the low to mid-$30,000's, if everything is in order. I would ask for more. You never know. Low mileage GN's are not hard to come by. I think one would be hard pressed to meet my expectations for anything north of $25,000. But then I'm not in the market anyways. Good luck with the sale of your car.