Indie game dev Jason Rohrer (Passage/The Castle Doctrine/Cordial Minuet) recently had a forum post about his income. I'd link to it but he's requested people not link to the Cordial Minuet forums:

We made $140K from The Castle Doctrine (and other games) in 2014. We made a bit more from TCD in 2013 as well, with the grand total somewhere up near $180K.

The TOTAL tribute received from all Cordial Minuet games so far is $683.4939. Of course, I also paid out $420 in prize money for the first tournament. Thus, the total income is only $263.49. I've been actively working on Cordial Minuet since June 19, 2014.

Cordial Minuet is my 18th game. I made 12 games that made nothing or close to nothing. My 13th game brought in a few thousand dollars. My 14th game brought in about $100K. At that point, I had been making games for about 5 years, and trying to make a living from independent software for about 7 years.