On average, how much money does an independent filmmaker make in a year?

About minus $100,000?

That's like asking how much a starving painter makes in a year. They could be living fat one year and scrounging for bread crumbs the next year. If you're looking to make money as a filmmaker, Hollywood is always there as an option which has lots of money to go around. Most independents are there to make quality films (at least that's what they say).

I remember once reading (I think on a site describing film programs) that many directors (espeically just out of Film school) will "make" as little as $20,000 a year. But that's if you are actually working, rather than making films. Making films costs money. Lots and lots of money (the few truly indie guys I know work second jobs as well).