Aha! There is a Prime Day e-book offer also.
https://www.amazon.com/Kindle-eBooks/b?ie=UTF8&node=17025012011&ref_=pe_2629530_245782890
QuoteBuy a Kindle eBook today, earn 40% credit back towards your next book, up to a maximum of $20. Offer valid only once per customer.
Credit must be redeemed by July 25, 2017. Credit can be redeemed on Print books sold by Amazon.com and Kindle eBooks.
You have to be a Prime member for this one and it's only good on the US site, I believe.