I have been experimenting with Amazon's API to try and find deals on Kindle books as well. Unfortunately, the API doesn't seem to let you search for books that are 100% discounted nor do they return the Kindle price. Instead, I settled for discounted books that are under a dollar. I have spot checked several dozen of these and all of them are only discounted for a limited time.
I apologize for the horrible HTML straight out of the 90s. If you are interested in more genres and/or sub-genres, just email me at Joshua dot Gatcomb At gmail (hopefully that defeats the spam bots).