A good place to get used books is paperbackswap.com. A lot of homeschoolers use it to find kid's books and even some workbooks. What you do is post books you have that you are willing to trade and for every one that you send to someone you get a credit. With a credit you can order a book from someone else. Your only cost is postage, and you send books via media mail, based on weight, and it's much less than the cost of a book, even a paperback, new. If you are lucky enough to have someone order more than one book at a time from you then you can get more than one credit for one mailing. I love it and it keeps even avid readers like me rolling in 'new' books all the time! As soon as you finish one you can post it for the next person to find. Join our book club and swap used books for FREE - PaperBackSwap.com