Sounds like a good price, but I'm always wary of good prices for things like this. Another member had his GS fully resprayed in its original colour recently and that was about £6k. About right to my mind for this sort of job. One thing you can guarantee - whatever you spend will not be recouped. It might make the car mor saleable, but there is a very limited market for early 4200s with almost 100k miles. If the car is a keeper then spend what you want to get the car as you want it and pay no heed to the resale value of the car.