Entombed was I think the most widely sold game at 500 sales within the first two years of release. At 40 usd each, that's 20000 dollars, which sounds like a lot of money but when you split that over two years work, really isn't, ----- afterall here in the Uk the minimum wage is twelve thousand pounds or about 18 thousand dollars a year.
And of course that's not counting whatever developement resources Jason had to buy to create the game in the first place.
The only developer I've seen who potentially could! make a ful time living from selling audio games is actually Aprone, sinse if you sold 200 copies of an audio game at 25 usd each that's 5000 usd, and if you sold five games a year at that wrate, you'd just about be able to afford enough to live, though not much more above minimum wage (at least the Uk minimum wage), and that's assuming that the resources needed to actually develope the games aren't too much themselves.
I do here that the Shard workshop boys who created Zero site are trying! to do audio game developement ful time, but how successful this will be I'm not sure, though I deffinately hope they do well sinse Zero site was a very promising first game.
In fairness though these are probably the worst economic conditions for anyone trying to make an independent living out of entertainment, sinse the economy of the world is going to hell in a hand baskit.
I personally just hope that sorts itself out before I've finished music school, sinse it'd make making a living as a professional tenor extremely difficult.
With our dreaming and singing, Ceaseless and sorrowless we! The glory about us clinging Of the glorious futures we see,
Our souls with high music ringing; O men! It must ever be
That we dwell in our dreaming and singing, A little apart from ye. (Arthur O'Shaughnessy 1873.)