Aslong as it's in good condition, I'd say a little short of 4 grand is a decent estimate.
The top is an expensive part and on this old of a car, it has a tendency to deteroriate unless well-cared for and garage-kept. The rear "window" can also become cracked and foggy, so check that out closely too.
From there, just use good judgement, as it's just a cra like most others. But if there's something wrong with one of the doors, inside or out, be prepared to hsell out a bit of cash because they're 'vert-specific parts.
