This is the situation facing people in these two professions nowadays, according to American journo and editor Jules Older, and now psychology academic at the University of Otago, interviewed on Radio NZ on 17 August. Archived audio file.
In the past if you knew your subject you could make an adequate living from both, but not nowadays: pay rates offered - from small publishers to the likes of Fairfax and ACP - are pathetic. (This though is probably self-defeating for the likes of Fairfax - the old saying is "if you pay peanuts you'll get monkeys". Who wants to read pieces written by monkeys?)
A website for journalists in this situation.
For book authors and illustrators the same financial straits apply, but here few have any illusion that they are going to make real money from their book, the motivation for most is different.