Take a bachelors in Mechanical engineering and a bachelors in philosophy.
Say ME is more in demand. Keep those costs for ME "high" while increasing public funding for students interested in said field (using the money leftover from the fields in low demand).
Lower the price of the low-demand field (philosophy in this case) while decreasing public funding.
Cost and funding will fluctuate as does demand
Feel free to destroy, adjust, or come up with a better idea.