The science of pricing a book is evolving. In the good (?) old days, publishers decided what an author's book would sell for and they pre-printed it on the cover. They would often show different prices for different countries on the same label and assume that the exchange rate wouldn't change. All of this was tantamount to price fixing, but the bottom line was that the content creator had no control over what the reading public paid, and their own income was decided by someone else.
The internet has changed all of that, along with everything else it touches. As authors have begun to find new ways to connect with their audience, and new formats ( e-readers), they have taken pricing into their own hands. The old-line publishers are resisting the change, and in many cases they are keeping their author clients in check by maintaining an artificially high price for e-books. However, as bestselling authors from the legacy publishers discover the freedom and economic advantages of controlling their product ( that is, self-publishing) the pricing of books will begin to find a common ground.
Jackie Collins announced today that she is re-releasing one of her best sellers as an e-book at $2.99. I think we will find that the pricing will almost always be under $9.99 as we move forward. It is just a guess, but I think the "big guys and girls" will start offering their new releases around that price and the rest of us will begin to slot ourselves around that standard.
Once the Stephen King's, David Baldacci's, Dan Brown's and J.K. Rowling's break from the legacy publishers and decide to strike out on their own, the price formula will become much more obvious, to the great good fortune of the reading public.