Here's a post I did on "Money Matters" -- the most interesting parts are the links to trad authors where they discuss earnings. Most of it is a few years old now, but it gives you some idea of what they earned/look to earn:
http://www.bearmountainbooks.com/fav...money-matters/
This post has a couple of other author viewpoints:
http://www.bearmountainbooks.com/fav...more-on-money/
There was one more post, but I can't locate it at the moment. I'll add it here when I find it. I can't think of the title of it. I discussed more of my own earnings in it, but you get the general drift from the above post. Here it is, but again, it doesn't cover much that the other posts don't. There may be one other author listed who posted some stats (V.J. Chambers):
http://www.bearmountainbooks.com/hom...a-new-and-old/