AmblingBooks has a lot of audio books discounted at $6,99. Unfortunately, many of these are not available for me due to georestrictions, but someone else might find the sale useful:
You can also find some discounted books in the non-fiction genre.
Just to mention that I haven't bought anything from AmblingBooks, actually, but I downloaded their Android app some time ago and I had to register. I learned about the sale from their e-mail.