first, Bibi did not go to a public school, but to Sloan (the MIT school of management), which is a private corporation.
you should also keep in mind that tuition is about 30,000 USD per year in any major league university (40,000 in Sloan), and that living expenses are extremely high. it is not enough just to look at tax, PPP and expenditure.
keep in mind that the tuition is based on supply and demand (among other things)