Back End Developer - Amazon Product Advertising API Needed

Hello all - I'm working with a client on an ecommerce site for their textbook rental company. I had been working with a back-end developer who has since not worked out. Most of the user interface HTML/CSS is coded and ready to go but we still need the basic back-end stuff. The client wants the site to use the Amazon Product Advertising API to generate most of the information when a user searches for a book (i.e. descrip, ISBN, cover photo, etc ). If the book is in their local inventory, then a link appears that says "rent me" and then they can proceed with the local checkout process. If not in the local inventory, then the link says "Buy from Amazon" and they are redirected to the Amazon product page using the client's affiliate code so they get credit for the sale. In addition, the original developer was supposed to do all the admin functions/logins, customer logins, checkout process, search function, etc. We originally identified the Spree open-source solution to integrate all of these functions for the client, but I'm open to another way to tie it all together and give the client access to the admin side. I appreciate your interest!