Good luck with the sale, Gary. $10K would be nice and not unfair, but $8500 is a pretty solid offer for that bass, as beautiful and well-appointed as it is. It's never easy to get money back for options that appeal to the original owner and may not be important to the next buyer. The market for a 36 five string probably isn't the largest, so there may not be crowds of motivated buyers out there to bid up the price.
I guess what I am saying is that you shouldn't be disappointed if you have to take the $8500.
-bob