You might want to check out the NY Times archives. Most local libraries subscribe to the Times.

They have an ongoing feature where they break down how various City residents live on their salary. I think the last one I saw was a college professor living on $130,000/year and someone else doing it on $40,000.00

Another thing to remember is that there are a lot of things that residents know/use that tourists are unaware of. Half price or free access to shows, free admission to museums for residents, sample sales, etc.

Finally, many people work in the city and are willing to take long commutes. I know folks who live in Pennsylvania and drive two hours each way every day. another guy had his family living out of state; he'd sleep at his mother's place five nights a week and spend the weekend with his wife and kids.