San Fransisco perhaps isn't going to work well for somebody who wants to live on their own and save money, but they are the outlier there. It is trivial in Seattle, and not hard in NYC if you don't insist on Manhattan. I know people who do it in Boston and Chicago (until recently anyway, and technically he was making "ethanol engineer" money, not "tech" money... I digress though.)

I am not very familiar with San Francisco, so I left myself some wiggle room ("(at least in most of those cities)") but having a roommate is not a requirement for anybody making a tech salary and wanting to save money in those other cities.