it's correct to think about the bigger picture, but you'd be paying rent anyway. I think the right number to look at is tuition + opportunity cost, e.g. 6K + 18K salary or whatever.
Opportunity cost was very little for me and all the other CS people I knew in undergraduate. The alternative for most people was doing tech support and making 24K/year with no growth potential (using local rates). Since the local rate for a BSCS is about 50K, there's no meaningful reason for the bulk of students to drop out. You'd have to have 20% year over year growth in income (not counting the bennies coming in with a salary job) to equal it.
In other words, for a computer science student - if you have a business raking in cash and you need to drop out to keep the money stream, you're losing out. Otherwise, stay in college.
You can live on about 1K per month. So loosely, that's about 20K per year to get a degree here.