Well, mostly free! You pay to ship your book to someone when they request it and in turn, you can request a book! Win-win! I just found the PaperBack Swap online and am excited about swapping our already-read books for some good books for the boys.
I just requested two books for the boys and have a wishlist set up for more. Please use me as your reference if you check it out and sign up; I get a free book credit when you do.
