Hi there
We are beta testing an ecommerce catalogue for use with Moodle. It supports Paypal and would let you sell books (or anything else for that matter) as well as the course enrollment.
If you would like to see an online demo - access www.instructionaldesign.co.uk.
More info is at http://www.connectedshopping.com/ecommerce/webshop/elearning-solutions.html. If you use our contact form, you can request access to our beta program.
Many thanks
Richard