I did the analysis for Princeton once - the average out of pocket cost was $15,000 per year. That has remained constant even as sticker prices (and the cost per student) has escalated.

What people don't appreciate is how much expense per student has skyrocketed in the last 20 years. Princeton has about 100 more student sports staffers, and spends about $45,000 per year per student in student services. Library expenses have also escalated far faster than inflation.