I disagree with this plan. The only way to lower the real price of anything is to decrease demand or increase supply. The reason we have rising costs are because we have too many students going to college to get degrees they don't need and won't use.
We should change student loans to be more like other loan applications. You can't get a mortgage for a house if you don't have the income potential to pay it back. (Well at least you couldn't until the government stepped in)
If I was a bank offering loans to students and one was studying a field with a high earning potential like engineering or computer science, I would offer a high credit limit for school loans. On the other hand, a student getting a degree in 'general studies' is not going to be offered the same credit line because the reduced potential earnings after graduating.
This would limit students from getting degrees solely for the sake of having a degree as well as incentivize an education with earning potential. If there is a high demand for nurses in the job market, loans for nursing could be obtained easier than those for fields that are saturated like high school history teachers.