Have you ever been to a Library Book Sale? They are awesome. Books range from .10 cents to $2. Weymouth's Tufts Library is having one today from 9am-4pm. I think this one is just paperbacks. Anyways, the library sells off old books and donations to make money for their "Friends of the Library" fund that help do something or other for the library.
Other towns have them from time to time. I think Weymouth usually has one about every 3 to 4 months. I once picked up about 22 books at one of these events and it was like $3 for all of them. Craziness I tell you.