Bulletin board postings
Aside from the library, the school’s bulletin board is a great place to find textbooks for sell. This is a lot better than looking for books from the school’s bookstore, since most of the books being posted on the bulletin board are only from the past semester and students usually sell them at a much lower price. The only downside is that those books are very limited, and you have to constantly look for them before another student buys.
Unless all other options are ruled out and you must purchase a book for a class, there are actually several very useful websites that sell secondhand textbooks at a much lower rate. Some websites include Amazon.com, BookCloseouts.com, or Ebay.com. For an extensive list for discounted books, please check out this website, http://studenthacks.org/2008/01/23/used-cheap-textbooks/.