Has anyone evr heard of Paperback Swap? It is an online book swap club. It only costs for shipping when a sender is shipping books out, not the receiver. Credit for books are given initally when books are posted, and then when someone orders books.
I have gotton many free books. I have even got some free college text books for free! There are books for all ages, so it would be very useful for homeschoolers.
There is another options inthat there are very inexpensive credits that can be purchaced for those that don't want to give many books away.
There are a bunch of online book swapping clubs. This is the one that I am personally familiar with.
http://www.paperbackswap.com/index.php
For people interested in other free stuff, I have a free share blog:
http://freecycledelights.blogspot.com/