The answer is to build other accredited institutions that compete on costs. They can poach all those adjuncts from the established universities by offering them tenure-track positions, build no-frills dormitories, skip the fancy landscaping and neo-classical architecture, forego any formally sanctioned athletic programs, rely on the bare minimum of administrators, and focus on undergraduate instruction.

And that could be a decent second life for abandoned retail shopping malls, too.

It might also be nice for such an institution to adopt a libre-license or gratis-license policy for all course materials, such that textbooks and lecture notes are essentially sold for the printing and distribution costs, and electronic versions downloadable at no additional charge.

And since some of those new colleges will fail, establish a succession plan to begin with, so that the student records can be easily maintained and transferred.

Even if you cut established university costs to the bone, you still eventually run up against the problem that there isn't enough undergraduate instruction capacity in them to serve the growing demand for bachelor's degrees. You're going to need to build out anyway, and private universities aren't necessarily going to do enough of that if it drops the market price for tuition.