For the record, I’m not American nor live in the US, but I have a 19-year-old son who started attending the University of Chicago this year, studying economics. Just the tuition itself is $70k. My husband and I are lucky enough to be able to afford it - I still believe it’s an outrageous amount of money to attend college.
Generally students will get financial aid and scholarships that cover much of the cost of tuition, especially if they’re from a lower income family. I’m guessing that, as an international student from a wealthier family, your son didn’t quality for much aid. Tuition is also generally lower for residents of the state, which he also wouldn’t qualify as.
Even with all that it’s still incredibly expensive and lots of people end up having to take out large loans or work jobs while in college to cover the cost.