In my spare time, I help run a small, independent publishing house and we have seen so many strange price schemes from on-line book retailers. As brick and mortar bookstores have been declining, the distribution channels on-line have become a labyrinth of virtual warehousers, middle-men, print on demand companies, direct retailers, brokers, pirates etc. Our authors sometimes find their books for sale in on-line retailers that they never heard selling for wild prices that range from one penny for a new copy to tens of thousands of dollars for used copies.
Part of whats happening is that some on-line retailers have computerized pricing algorithms which use some mysterious formula based on the Amazon price. In some cases, a retailer adds titles to their offerings that they cant easily get so they price it such that no one will buy it (sometimes this process is also automated.)
The digital press revolution has produced some very strange things in the book world but it has also given us new capabilities. If you know of any out of print scuba books that are in public domain (over 70 years out of copy right) or if you own a copyright for an out-of-print or back-listed scuba book that you would like to see re-published, send me a PM. We might be able to resurrect it and make it available through Amazon.