Many public libraries in the U.S. are supported by their Friends of the Library groups. One of their prime fund-raising ventures is book sales. Such an event can be used to liquidate older versions of books from their collection and to sell books donated by citizens. These may include materials that can be valuable to your genealogical research. Older atlases may be useless to a library or a donor, but may be invaluable to your work. Reference books, language dictionaries, almanacs, local, state and national histories, older editions of genealogy how-tos, and other books may supplement your personal reference collection at a tiny fraction of the price of new books. Check with your library as to whether they or other libraries in your area sponsor book sales.