My personal take on backlist prices is that if the rights are owned by the author, the price is usually in the range $2.99 - $7.99, and $4.99 is probably most common. It's less than a new mass market paperback.
Publishers, on the other hand, generally never charge less than the price of a new mass market paperback. Their view is that:
- They want consumers to consider the cheapest paper edition and ebooks comparable.
- Any backlist book they publish is competition to their new books, and there's no point in selling a bunch of cheaper books that price conscious consumers will buy instead of the newly released book which hasn't made its pre-production costs and author's advance.
Sometimes, for "classic works", the publishers will only reprint in trade paperback because they don't expect to have a large enough print run to make it worth another mass market paperback edition. That's why you'll sometimes see 50 year old books get an ebook edition that retails for $12-15.