Where can I get a simple list of free Kindle ebooks?
what I think is, you can search it from amazon:
by selecting price low to high.
and also try the options given in this link:
MakeUseOf has published a few articles on this topic:
How To Download Free Amazon Kindle eBooks To Your PC
12+ Sites Every Kindle Owner Should Really Know About
Additionally, Mashable has compiled a list of resources to get free Kinde eBooks.