For free kindle e-books to download on Amazon, go here for public domain and here for non-public domain. There’s some good books so, you can save a whole bunch of money with these free e-books instead of paying for them.
The price searches on jungle-search are customizable, so you can also use it to search for bargain Kindle titles as well. For instance, you can currently find almost 30,000 titles available for under a buck, and more than 125,000 costing between $1 and $5. Just remember to filter out the magazines and newspapers, since they’ll bill you on a monthly basis.