When Steve Joiner attended the University of Colorado in Boulder in the late 1980s, his parents—an Air Force mechanical supervisor and a teacher—paid his tab of about $4,000 a year, roughly $8,600 in today's dollars. He earned a master's degree and became a high-school math teacher.

In August, Mr. Joiner's daughter Akaysha, the valedictorian of her high-school class, enrolled at CU, as the big campus here is known. But tuition, room, board and books for in-state students is now...