With the this FREE app, you can scan a book or enter an ISBN, and the app will tell you the current lowest price of the book, BOOK or kindle at amazon com.
You can also search for books on a particular topic, like say spiritual ebooks

The FREE app has a simple user interface that lets the user enter keywords or a book’s ISBN (international standard book number—a 10- or 13-digit code that uniquely identifies a book) and then lists the title, ISBN, and lowest price for a new copy at Amazon.
It also uses the Bar-code Scanner so the user can scan a book or E-BOOK. The App also regularly reccommends and reviews popular books and e-books on kindle, so you always have something great on your to-read list.