It seems that a number of online booksellers have resorted to algorithmic auto-pricing. See, for instance, this story about an $23,698,655.93 book about flies on Amazon:
A few weeks ago a postdoc in my lab logged on to Amazon to buy the lab an extra copy of Peter Lawrence’s The Making of a Fly – a classic work in developmental biology that we – and most other Drosophila developmental biologists – consult regularly. The book, published in 1992, is out of print. But Amazon listed 17 copies for sale: 15 used from $35.54, and 2 new from $1,730,045.91 (+$3.99 shipping).
Funny things happen when you let programs determine your book prices for you.