The professors friendliest to student budgets even separated their custom materials into "lecture notes" which contained only instructional material and "exercises" which were generally made up of problems that actually appeared on previous exams, including space to write in. Total cost for this style of "textbook" per course was less than $20, purchased new from the university bookstore. Or you could inherit an older copy of the notes for free and just get a new copy of the exercise portion.

That kind of thing would be a free download today. Can you imagine paying thousands of dollars in tuition for a course, and then getting the entire textbook for free?

Those who do it are truly saints among scoundrels.