When I got my BS in Microbiology 1980, an average, non-major, textbook cost $12-$15. At the time we thought that was excessive. All of my Microbiology courses at UNC were actually taught within the UNC School of Medicine, so you paid Medical School texbook costs. Those were exorbitant at $25.
Nowadays, with two daughters just out of college average textbooks go for in excess of $125 and up (and up and up). I haven’t a clue what Med School texbooks go for nowadays. I remember seeing the two volume set Texbook of Surgery going for an exorbitant $75 in 1980. I shudder to think what it goes for now. “sell the car honey, I need to get the Textbook of Surgery for next semester!!!”
I earned my BS in Engineering in 1984. Non major used books were $20 to $30 and I had one new EE book run me over $300. That book was updated regularly and so was only good for a year and the book stores refused to buy them back.
I won't even get into the cost of my books for my Masters.
My econometrics text for this term was $180. The lowest I could find for a used one online was still over $100.