BTW: I check my local used-book stores for many titles - a great source of low-priced reads for your library.
Amazon.com has a service now where they act as a broker for people selling used copies of books. If you pull up the page for a book you are interested in there is usually a link to people who have the same book for sale used. It's saved me a lot of money in the past and it's easier than scouring used book stores.