There a are lots of projects that use the Amazon API to great effect:
http://mashable.com/2007/08/21/amazon-toolbox/
In particular, there is this project which shows deals on your wishlist:
http://amazondeals.ca
Unfortunately they webscraped instead of API.
Problem:
But the only problem is that that it is next to impossible to cross corrolate to find used book sellers that have more than one of your wishlist books in stock in order to investigate whether you can get combined shipping.
http://ask.metafilter.com/37477/Buying-secondhand-books-online-how-to-avoid-multiple-postage-costs
http://ask.metafilter.com/35260/Used-book-buying-guide
Response:
How hard can it be to search each book, list the used sellers for each wishlist book and find sellers that have more than one book in stock?
Reward:
Make your affliate links and host to see if you can turn a profit on your code.
Perhaps pledge too? My pledge:
