Librarians aren't able to make monetary appraisals, but we can point you toward some resources that may help.

Your Old Books
This guide addresses some frequently asked questions about rare and older books and their values.

ViaLibri.net
A book search site that can give you an idea of the current price range of books for sale.

WorldCat.org
This tells you how many libraries hold the book in question, and is sometimes an indicator of scarcity.

Antiquarian Booksellers Association of America
You can use the bookseller search feature on this site to locate an appraiser near you.