Has the
Audible kids' books sale been mentioned? It runs through August 27, seems to be open to nonmembers, and includes about a thousand books for $3.95 or less.
The section for older kids (about half the selections) includes many classics (
Mary Poppins,
Pollyanna,
Five Little Peppers, Edith Nesbit books, fairy tale collections, etc.). What I consider the best find is the Naxos audiobook of
The Once and Future King--some 33 hours including all five books, for $3.95.