This Yahoo News article talks about a service that will mail you small segments of classics every day, or more frequently if you desire. This is targeted at the short-attention-span folks, but there are some comments therein pertaining to the sale of newer material at "under $5 per title".
They say "The Association of American Publishers (AAP) said on Tuesday sales of e-books jumped 24.1 percent to $54 million in 2006, but that is still only a tiny fraction of the total U.S. book sales of $24.2 billion last year."
DailyLit can be found here.