Slate had a review of a new book called Scratch: Writers, Money, and the Art of Making a Living with has some great observations and information about writers such as Cheryl Strayed and the nuts and bolts of how much they earn from publishing their books.
I spent my twenties in writing programs. A small press published my first book in 1999, and have published eight books with a ninth coming out later this year. I spent my thirties teaching creative writing in a continuing education context (University of Washington Extension, Richard Hugo House, The Writing Center in Bethesda) or as a volunteer, and then spoke at the Associated Writing Program (AWP) on panels over a couple of years (2012-2015).
I learned that the writing industry (when it comes to prose) is predicated on – like acting – the starry-eyed concept that you too can MAKE IT as a writer. This means if you have the skills, you will pay the bills with publishing books. Conversely if you do not have the skills, you will not pay the bills.) Sitting at the book fair table at AWP I could overhear the gaggle of graduate students strolling past the small press table where I sat talking about agents, book advances, about getting out of school and really getting down to writing once they got a book contract. Some of these students had paid a lot of money for the training to be a novelist. Many programs cost more than 50,000 a year. They were looking at coming out of a two year program in debt more than 100K. They were going to be need a pretty generous advance on their first novel.