I think the way a lot of porn sites deal with "piracy" now is to simply watermark the images and videos with the website name; this way when (not if) the images are stolen they actually act as advertising.
As far as I understand, you can't remove the watermarks without editing the image itself using something like photoshop, which is very time-intensive, but don't quote me on that.
In a parellel to the book world... I don't think anyone would remove the author name or title from a book (after all how would potential darknet readers find the book), so therefore advertising is inherent in ebooks. In my personal experience, the BAEN model works extremely well.
For example, the free library/BAEN CDs:
There were some books by John Ringo (probably my favourite author atm) which I wasn't sure I would like and because I was very busy with life in general, I didn't buy them. At a later date, with some leisure at my hands I saw them on one of the BAEN CDs, read and absolutely loved them. So immediately, I went and bought the rest of the series and the e-ARC of the newest book.
Also, I can have free ebook versions of all the pb books I have, to put on my reader and take with me on holiday.
The pricing structure:
$5 is about £2.50 (about as much as you'd pay for a pbbook in a second hand shop here. So really, it's a piffle. I could afford that even when I was a underpaid and overworked PhD student.
With eagerly anticipated books, I usually buy the e-ARC ($15 = £8 about the price of a pb here in the UK), so again, pricewise it just is easier and more convenient.