I feel your pain. These pianos are very sought after. If you have the time, go shopping for one. That will give you an idea of what is a fair price.
Bear in mind there is great interest in getting these instruments for rebuilding, and therefore some discriminating customers will try to get you to sell to them for under $3,000 (an arbitrary number, my personal one was $1,000) because it makes little sense to pay more for an instrument that you will spend another $15,000 to $20,000 to put in top shape.
If you are able to expain the atmosphere in which the piano has lived, how much it has been played, the servicing it has received, the condition of the soundboard and pinblock and the piano plays decent, you should be able to sell for about 10% to 25% less than the price you find when you go shopping for the used ones.
Like with houses, dress to sell. Polish the pedals and get the piano tuned and voiced.
Good luck and enjoy the thing you need the capital for. I am sure it is worth it and a chance for an even better piano will come along in due course (maybe an AA, or a BB, which stands for bigger and better).
As for mechanics. I like the idea of a silent auction, where you set the minimum price you will sell for and tell your potential buyers that you will open bids a couple of weeks after you advertise in the paper in your nearest metropolitan area.