Estimate textbook costs and rental vs purchase savings.
Three routes exist for a reading list: buy new, rent for the term, or buy and resell afterwards. Renting is priced as a share of the new price, while buying and reselling costs the new price less whatever you recover. Which wins depends on resale value — editions that turn over quickly recover little, and rental then dominates.
Textbook routes
Rent total = books x new price x rental share/100; buy-and-resell net = books x new price x (1 - resale recovery/100)
Usually when resale value is weak. If you can recover more than the rental price by reselling, buying wins — that comparison is exactly what is shown here.
New editions and bundled access codes make older copies unsellable, which is why recovery rates of a third or less are common.
Course reserves and institutional licences can reduce the count of books you need to acquire at all. Lower the book count before comparing routes.