You basically said it yourself. They could just go to instate public schools.
I really wish I had done this. It would've saved me $20,000+. It's a great option, especially if you're in a place with a good community college system with guaranteed admissions agreements (e.g., Virginia).
Compared to what, the price of a hamburger? In state tuition can be 1/2 or 1/3 the price of out of state tuition at the same school, and state schools have lower tuition than a lot of other unis already.