Amazon does have used books for sale as well, and if you go to the site, it will tell you how many used books of what your looking for they have available.
I highly recommend books by claire weekes! I agree with the others here, try used at amazon, or e-bay. In my opinion, these books are worth getting!
I really liked her book Hope and Help for Your Nerves. I actually felt like she knew me and was my friend while reading that book. I know that sounds a bit strange, but it's true!
1. Go to Amazon.com
2. Search : Hope and Help for Your Nerves
3 Click on the book your interested in, as you can see they have used ones available or order new for $6.99 plus shipping no matter which you choose.