It costs $2,200 to live on campus at my college. That includes 1 semester living in one of 12 dorms, internet fee, meal plan for 1 semester, 50 channels on TV, water, electricity, heat, the whole nine yards.
The average apartment here is about $350-$500 per month. Add in food (I'd say at least $600 per semester), electricity (average $60 per month), water, Internet ($40 per month here), cable ($40 per month), and all of the other expenses of living in your own apartment. The total is at or over $4000 per semester.
I guess it varies depending on where you live and which college you go to. In my situation, on-campus living is definitely the way to go, and is the obvious reason why juniors and seniors aren't guaranteed on-campus housing. I sure as hell hope I get picked for on-campus housing next year (my junior year), even though I only have a 25% chance of getting it.
-Lasereth