I don’t make much money on eBooks (compared to writing ten books for publishers like McGraw-Hill, J. Riley, Springer Verlag, etc.) but I so much prefer self published eBooks - so easy to push updates and new editions! I have one eBook that sells very few copies (on the super niche Lisp Hy language) and I decided to make the minimum price free last month. The sales actually increased.

Anyway, probably the best model at least for me is to make eBooks freely available, but with an optional ability to pay for a book.