Can you look into graduate assistantships, research grants, TA position, or research assistant position at Columbia? Maybe positions that aren't related to CSD, like advising or housing? Some of the assistantships offer a tuition reduction along with a stipend, so that may help, even if it is a private school. I am in a similar position and as much as I want to go to my out-of-state dream school, the amount of money I would have to take out terrifies me.. Good luck with your decision!!