I've won awards and prizes in various writing competitions throughout my life. Both school and professional.
Including a Young Authors award I won for a book about a Dinosaur. (They published it, and everything.) Though I was very young.
So, I was thinking about writing commissions for people who want stories of their characters, but are otherwise unable to write or come up with anything themselves.
What would someone even charge for something like that? By Page? By Word? Or would it be a flat rate for a book?
Its highly variable, years ago one of the mega authors mentioned that many decades ago he got paid 1 cent per word, which if you think its pretty east to knock up a 5 thousand word chapter, is $50, an appreciable amount even today. If you charged per page, have a look round at all the mega books coming out now of 850-1050 pages, and these books can be part of a series.
Id say for the best idea is to look at a print on demand service such as Lulu, compare the prcentage you get, the percentage they take, and how much the charge for so many pages requested. Then compare those costs which can be well under half that of the multi mass printed main street books.
Only when the digital representation of the book is printed in the book, as well as the human readable text, as a digital scan, such as QR code, will books and online truely be comparable and interchangeable.
Good luck.
Its highly variable, years ago one of the mega authors mentioned that many decades ago he got paid 1