I could go into this subject for hours, herp books are one of my main hobbies (even more so than herps)
Best thing I can say is, good herp books aren't as common as you think.
the AVS books are more standard basic care guides, if you want specialized books on care of specific species, then 60$ is pretty cheap, books you commonly find especially in chain book retailers and pet stores focus on Shiny pages and glossy pictures, and not so much so on the quality of the data, which is usually recycled information.
If your wanting a good book on
corn snakes, wait for the Biology of the
corn snake book that should be out.. eventually (Notker Helfenberger & Klaus-Dieter Schulz)
The bill and Kathy Love book would also be a good one "cornsnake manual"
It just depends on exactly how detailed a book you are looking for.
as far as ball pythons, there is the Barker book
pythons of the world volume 2 which focuses on Ball pythons.
volume 1 was excellent, I have not yet seen volume 2, but I would guess it would be as good if not better.