"slums seem to need a combination of cheap housing and proximity to unskilled jobs that pay by the hour"

Actually, they need cheap, undesirable housing, and not much else. Slum neighborhoods are more often characterized by their _lack_ of job opportunities, pay-by-the-hour or otherwise. This is one of the things that makes escaping a slum so difficult -- the need to pay to get to any kind of work that enables you to live.