I believe the value of money in these recessionary / inflationary times is less and less each day. While not necessarily free, there are quite a few Kindle books offered for just one to two pennies.
The titles seem to change frequently, and I don’t know if that is intentional on Amazon’s part of a server error. Looking at what is available right now, there are about 200 available in the penny range and include mysteries / thrillers, romances, health and fitness titles, and foreign-language books.
I’d recommend you save this shortlink and check it out periodically: https://geni.us/1cent
Good luck and have fun!