http://www.textbookleague.org/103feyn.htm
I for one welcome the day when all textbooks are open-source eBooks (preferably written by people who are deeply knowledgeable and passionate about the subject), or when the Khan Academy model is widely adopted, making textbooks largely obsolete.
Programming Languages: Application and Interpretation is freely available from the Shriram Krishnamurthi. (http://www.cs.brown.edu/~sk/Publications/Books/ProgLangs/). I can vouch for Shriram being one of the most passionate educators I've ever had the pleasure to study under. Nevertheless, as a university professor I don't imagine that he's Warren Buffett rich.
Likewise, Professor Geoffrey Grimmett distributes 'Probability on Graphs' on his website (http://www.statslab.cam.ac.uk/~grg/books/pgs.html) The PDF version is actually better than my print copy, which contains an incoherent index.
http://learncodethehardway.org/
I've never heard that Zed Shaw is a billionaire so I guess that's not a requirement to produce top-notch educational content.
If Zed Shaw and Salman Khan can produce this stuff (mainly for the love of doing it, or so it seems to me), then why not many more ordinary people?
If people are motivated enough to work on operating systems in their spare time, why not on kick-ass educational content that doesn't suck and cost a fortune doing it?
I don't really want medical textbooks produced by ordinary people. I want them produced by geniuses, and checked by other geniuses.
Make an awesome outline, do a few chapters and rather than go to a publisher, go to kickstarter and lulu.com.