Obviously the price of textbooks isn't the ultimate bottleneck for learning stuff. But, there are important difference between free & cheap. Easier access has all sorts of catalyzing effects.
For example, a free textbook can be referred to. "For a more detailed discussion of this read chapter 4 of Gaussian Processes for Machine Learning."
For example, a free textbook can be referred to. "For a more detailed discussion of this read chapter 4 of Gaussian Processes for Machine Learning."