Decoupling education from certification would work. Most people are willing to pay so much for college because they need certification; they're forced to pay for the education, whether or not they actually learn anything.
The Federal government could mandate that any school that's eligible for funds has to make the certification open to anyone, and also make sure that the certifications themselves around coupled together (you don't need a certification in Art History to get certified in Biochemistry). If people can pass the Harvard certification for, say, Harvard Astrophysics, then they get a Harvard Astrophysics degree the same as someone who took classes at Harvard and passed the certification.
It's known that bundling items together is usually a good way to force people to buy things they don't want. People talk about this all the time when it comes to cable bundles. But our higher education system is based on bundling a lot of things together, so when people are trying to acquire what they need, they're forced to pay for many things they don't.