Its good that you’re in GS. They allow part-time status, and you are able to major in the same things that the CC/Barnard students do. Graduating from GS with an economics degree will be highly valued. Even better if you were to do something like CS.
You might want to contact the Columbia Career Center (CCE) and tell them you’re an accepted student and wanted to know what were career outcomes and starting salaries for econ majors. They post some general statistics on the website (see below): Data & Statistics | Columbia CCE
But I’m still unclear on how you are going to pay $45k per year for it. Thats a lot to take out via private loan, unless your family is willing to co-sign. But if you get a good job after college you’d be able to pay that back fairly quickly.