New York IS cheap. If Williamsburg is too expensive, go another subway stop out to Bushwick. If that's too expensive, go another subway stop out. Take an extra ten minutes on the subway and enjoy thousands of dollars off your monthly rent.
NYC is absolutely enormous, and there are parts of Brooklyn and Queens that have grown CHEAPER over the past few decades. Admittedly, that's because the criminal elements of NYC have been concentrated there... but cheap is cheap.
NYC is unique among American cities in that our subway infrastructure allows ENORMOUS expansion of affordable housing in virtually every direction at no financial expense and almost no sacrifice in time. It's cheap as hell to live in the South Bronx, for example, and you'll get anywhere in Manhattan relatively quickly. San Francisco simply doesn't have the same flexibility, since the transit there is so god-awful by comparison.
Artists don't get to live in the Upper West Side just because "art!" Go live in edge neighborhoods, of which there are plenty. If you want to complain that neighborhoods are increasingly less walkable and more dilapidated the further out you go... lobby to allow developers to build new, dense buildings out there. The only solution to expensive housing is to build more housing.