I've been publishing a series of "One-Buck" e-books about publishing. The books are deliberately priced low to encourage people who are even remotely interested in the topic to take a chance. I hope that readers will be so impressed that they'll buy more of my books.
When I tried to publish my book about typography, I wanted to price it at one buck. I was surprised when Amazon's KDP (Kindle Direct Publishing) system gave me a message that the book had to be priced at $1.99 or more:
accepted and published using KDP.
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So, I raised the price to two bucks. It's still a great value.
If you plan to publish a large but inexpensive e-book on multiple platforms, be aware that the price for the Kindle may have to be higher than the price for an EPUB. That's silly. It will be better to raise the price of the EPUB to match the Kindle, or reduce the size of the Kindle book.
If your book is all-text, you probably won't have to deal with this issue, but if you have lots of artwork -- like my book -- the Kindle requirement is important.
By the way, my new book is terrific, and will be very useful for any author who wants to format pages, design a cover, or just better understand what a professional designer will be doing. The book has been in the top-20 of Kindle books about typography since it came out. I'm impressed.