To answer your question, I dont really know. I saw one new book on amazon, about $2000, not sure someone will pay that price. and I am not from the states, so ebay or amazon is not an option.
I wonder what mine's worth...I got marks, written notes, highlighted stuff throughout. I don't think that would matter much because the material itself is what makes it valuable. I know it's worth a whole lot more than the $200 price we paid for it then.