My entire stock of ebooks are on sale for 99 cents at Amazon (one exception is the 3-book volume which ends up costing 99 cents per book + 2 cents to reach the $2.99 mark for 70% royalty).
Several of these books are on the Kindle Unlimited program, thus are free to subscribers.
At Smashwords, a few of the same books are free (because they let you do that on Smashwords).
At Barnes and Noble and Kobo, the same free ebooks at Smashwords are free on these sites as well.
These prices will be good until the end of the month. At that time, they'll be raised to something reasonably within the parameters for ebooks, mostly $2.99 for the 70% royalty point on Amazon.
All the books are also in print with very low prices on them all. To keep the price point at minimum, the sale prices are only available on Amazon.
Oh, and several of the books are also in audio format and sale priced at $1.99. You can get them through Amazon or directly from Audible.com.