In accordance with signalling theory, for cheaper or free credentials to get any traction, obtaining them will require a very significant investment of time and effort.

Kind of like a degree.

Traditionally, if you wanted to become competent, you went to trusted school, worked hard at the course of study provided by the school, and if you completed the course requirements, you got a degree in which the school declares you competent. This was expensive because it was expensive for the school to provide a course of study that made students competent. The school needed to pay for great teachers as well as materials (books) and facilities (libraries, labs). Great teachers, materials, and facilities could not be found except at the expensive schools. The school also tested students but testing made up an insignificant part of the total expense.

Now the costs of providing the education is going to zero. Instead of highly paid teachers lecturing tens of students at a time, Sal Khan is making video lessons that are viewed by tens of thousands. Instead of expensive textbooks, Wikipedia provides better information for free. Instead of recitation hours in a classroom, students are tutoring each other online or testing themselves with flashcards.

Traditional educational institutions are being left with a shrinking value proposition. They screen students (admission). They verify that students are doing the work and learning (testing). They graduate students (certifying). These functions are not what traditionally justified their high cost.

Of course becoming competent requires significant time and effort on the part of the student. But this doesn't mean that the means used by the student need be expensive. One can become very physically fit without joining an health club and hiring a personal trainer.