How much should college cost?

How much should college cost?
Making the math simple here: let's say one professor teaches five courses, each course has 20 students.  Each student takes five courses per semester.
Each student pays 1/20 of the professor. If the prof makes 80K/yr then tuition should be $2000 per semester. Or $16K for a four year degree. 
I understand this would be only for subjects where it is all classroom, such as Math, History, Literature, and the all important Liberal Arts.  
I also understand that this does not include "overhead" such as classrooms, library, dorms, cafeteria, etc.  I believe that donation should pay for buildings, not the students.  And doing the math for classrooms and such, it comes to a relatively small amount, like $200/semester.  
Technical subject like the Sciences would cost more, due to lab costs. 
Athletics pays for itself, thru ticket sales. 
Library should be paid for thru donations from alumni.  
That is how much college should cost.  But even in-state tuitions are triple this.  Go figure.