A lot depends on the definition of rebuilt. At that price they better have replaced almost everything that moves and some things that don't.
Nine foot pianos are dogs to sell. There is very little market outside of some institutions and concert halls. Of course actual selling price will be influenced by whether it is a dealer or private party, but I would not be afraid to offer quite a bit less. Exactly how much depends on a lot of intangibles we, here, do not know.
There are few joys in life greater than the absence of pain.