This is by no means a definitive guide to piano values. The true value of a piano is determined by how much someone is willing to pay for the piano. So, to begin, one needs to have an idea of what a piano like yours is going for -
Keep in mind that how much is being asked for a piano in a store or on Craigslist is not necessarily what the piano will actually sell for. In my experience, most are highly over priced, and do not sell, or sell for substantially less. One cannot compare their piano to the price of that in a retail store (which is what I see) as retail pianos usually have been refurbished, serviced, include some kind of warranty as well as a tuning and delivery.
If one would take two pianos, set them side by side and there is actually no difference between the pianos, it's going to come down to sound quality and mechanical condition to a serious player - the better a piano sounds and performs, the more musical value to a player will win every time, regardless of how the piano looks.
I also hear people say that they have been told their piano is an antique piano that would be worth say, $20,000 restored. It can cost $15,000 to $18,000 to get that piano restored.
Think about it for one moment:
I have ample opportunity to rebuild and restore antique pianos, but there isn't a line of buyers waiting to get one, especially for $15,000 to $20,000. So I don't spend time restoring antique pianos. (I'd love to, but I need to make a living). The lack of rebuilt antique piano buyers along with a $15K to $18k investment to restore a piano only leaves $3,000 to $5,000 margin, which isn't that great of a return if the pianos did have a decent market.
The bottom line is used pianos are not rare, but used pianos in good to great condition are rare. Almost all need work to get them to perform musically, as age, neglect and deferred maintenance have accumulated over the years.
The value and price of the piano depends mostly upon its ability to perform musically - that's what the market will bear.
As for sentimental value, that is a completely different topic.....
Notes From the Piano Bench
Questions and Answers and updated factoids concerning pianos in the 21st Century.