I hope you'll be able to find some good deals.

Most of these websites use algorithms to track book price drops on Amazon, so they actually link you to the book's purchase page on Amazon. You buy it just like any other ebook for Kindle. As far as the prices, usually they don't list a book unless it is on sale for $5 or less. Most of the time they are $1.99. I know I picked up the book Hidden Figures for $1.99 right before the movie came out earlier this year, so I got to read it before seeing the movie which was very helpful and informative.