I wrote one book (technical, on a hobby subject) which brought me a few hundred dollars (not much but it is in a highly specialized domain and there was very little marketing). I worked with a small editor (who covered all costs except for my time), asking to do most things myself (which they accepted after seeing a draft), and it has been a really rewarding experience!

I used Latex for the editing (giving me a very polished final look, something where most self-published books fail at), did the illustrations myself (drawings, done using photographie and a vector drawing program: the result has fooled some professionals into thinking I am great at drawing), had an army of proofreaders (almost a dozen with various degree of knowledge on the subject matter, paid with a copy of the book, all of them found numerous mistakes) and even a lawyer (for advice on some copyright fine details as the book contains translations from other authors).

Overall I would reommend the experience and will likely do it again (the next step is being in control of the marketing aspect).