It's terrific that you've found a private school that would cost $20K total for four years but everything that I've read indicates that such a school is a
tremendous outlier. The average tuition for a
public school last school year was $5500 for in-state students and $12K for out-of-state students; private schools tended to be substantially higher.
https://www.collegetuitioncompare.com/statistics/
Anecdotally, the college I went to, New College of Florida, is a public liberal arts school whose costs aren't too far out of alignment with other state schools in Florida. According to their fees page, in-state tuition fees, room and board would total $16K a year; for out-of-state students, that would be $39K a year.
https://www.ncf.edu/admissions/tuition-and-fees/
Actually, I'd like to gently question your figures: you're indicating your kids are paying $2000 a semester -- so that would be $4000 a year, or $16,000 over four years. And you're saying that doesn't include their tuition, so that's just room and board, right? (That's under half the cost of New College's, which again sounds like quite a deal.) Further, room, board and tuition at this private college would still be under $20,000 over four years? Unless I'm missing something, that would mean tuition at this private school is less than $500 a semester. I can't help but suspect that either one of us has our math wrong, or you have the best school deal in the history of ever.