@benjaminlefort also self-published a book, and his second is either on the way or very recently published. Both are in the personal finance arena.

Personally, through Medium I got requests for content that pay up to $500 per post (though most are for somewhat less).

This also gave me an idea for a website-based service that may end up scaling a lot, but at this point I'm just working it out, so too early for details.