I've seen a lot of questions on affording/finding book choices and wanted to put up a general category for how to find cheap books!
1. If your local library doesn't have it, you can often request it from another library in your state for free or a small fee--I do this all the time. It costs me 75 cents. This works especially well for literature books that we can read fairly quickly.
3. Use http://www.paperbackswap.com --use the wish list feature if the book you want is not available right now. I often get books there, and the average cost to me is about $2. I just ran through my list of transactions there, and quit counting at 150 school-related books I got there!!! I often list my books I won't be using again there to trade. Stop by and say hi! I'm Bookwormmichelle there.
4. Don't buy new if you do buy. Attend used book swaps or library sales, use places like Amazon Z-shops and half.com, check online cutrate places like buy.com or bookcloseouts.com
To find book sales near you, go to http://www.booksalefinder.com You can register there and they will tell you what is coming up in your area.
To find prices on books from many sellers, try Fetchbook at http://www.fetchbook.info/ Enter in the book you need and it will automatically search many sellers to find you the best price.
Just watch out--if you try all these things, your house might end up looking like mine--decorated in Early Messy Library/Insufficient Shelves Style. :0)
Michelle D