The hard part about putting a value on pianos is what they retail for and what you can actually sell one on the open market, are usually two very different things. Regretably, Craigslist has dozens of them that people can't even give away every day. The problem is that in order to be sure your getting a decent one, a buyer really has to have a pro come by and check it out, and the cost of transporting one by a mover is several hundred bucks. Then tuning is about another hundred, once it gets to the house. So there are a lot of big costs involved with the purchase, in addition to the purchase price.
Also the reason why a piano should be checked before it is purchased is that there can be a lot of hidden problems in a piano. Its just like buying a used car. I once bought a beautiful old upright, that had pegs that had been worn down and it kept slipping out of tune. So the unscrupulous piano seller that I bought it from hammered them into the holes in the tuned position. It was in tune when I got it, but it could never again be tuned. He ended up closing up shop and running out of town with a truckload of pianos! In the end, I ended up donating the piano to charity. I now have a wonderful old player piano that is a lot of fun.
If you're trying to sell it, you might consider getting it checked out first, and then you can have that piece of paper that gives your piano a clean bill of health. That would be a big selling point that might help someone pick your piano over another. Another selling point is the piano's tone. Like all wooden instruments, they are as individual as the trees that they come from and they all have their own unique voice. Although again, if you are selling, someone buying a piano, lets say for a kid's first piano lessons, might feel that all pianos sound the same.
So if you're looking for an insurance value, or just want to know about it because you love it, we can try to locate similar pianos and get an approximate figure. But if you're trying to sell it, all I can do is wish you the best of luck in this economy!!