I ran across an article recently, suggested by Jeff Henig from Facebook. The article, from informationisbeautiful.net, is based on British royalty rates and info... but I believe it is still a good overview of the industry in general. The question is, how much do you have to sell to receive the equivalent of minimum wage? It's not very encouraging. As Jeff said in his post, "food for thought."
How Much Do Music Artists Earn Online?