Through June 30th, select accounts at Amazon can get a $3 credit on select Kindle Books. If you are eligible for the offer, you just need to click the button to add the credit to your account.
After that, click on through to see the included books. There are 44 different ebooks available that you can choose to use the credit. Prices start at $3.99, so with the credit, you can get an ebook for as low as $0.99.