The back list is an increasingly important revenue source in the age of ebooks because a) new readers can easily buy all the books in a series, and b) owners of paper books may buy again in ebook form.
A common way for publishers to mine the backlist back in the paper book era was to reprint omnibus editions, collecting several novels into one book. This gave readers a bargain price overall, and presumably was profitable for the publishers (otherwise why do it).
As an example, there are now three Harry Bosch collections each containing three novels. When only two were available, Hachette set the ebook price an $9.99 in the US and $11.29 CA (see
Three Harry Bosch Novels Shortcovers). This was an good deal, and I bought both even though I had read all of them in paperback. The third is now available, but the price of all three collections has been raised to $17.99-$19.99 each. The third collection has a 1 star rating in the Kindle Store because of price.
This is still cheaper than buying the three ebooks separately, but is $19.99 the right price for three back list tiles in one ebook?
The Harry Bosch volumes clearly started out as paper books. However, it is very easy to combine ebooks into collections. Is this something that publishers should do more often?