Kobo has an informative post on customers' buying habits versus publishers' wishes. Apparently $11 is the die point for buyers. That's how much we want our books to cost, and after that our willingness to pay drops off significantly. Actually, I think $20 is my die point (remember I'm in Australia, our books are strange prices). To pay more than that the book generally has to be non-fiction. You'll have guessed I buy paperbacks--price, shelf space and carry weight are all factors against hardbacks.
[Article mentioned on Dear Author]