Apples and Oranges
You wanting to buy an article online is not the same as a textbook a student needs for a class. In your case, I'm reasonably certain the authors of the article are in the compensation loop, they are using the publisher as a distributor. In the case of the student, I agree that textbook prices are a rip off. When they price themselves too high they will create competition. Competition naturally moves to where profits are higher than normal, in this case it would be illegal competition: The enterprising student who scans the textbook and sells it at half price to fellow students.