when it comes to textbooks, my thing was if the teacher isn't assigning assignments directly from the book then don't worry about that exact book.
the books all contain the same recycled info. it isn't like one economics book is going to hold some secret unique info the others don't. if they are on the same topic they will teach the same general thing just in a different way. this worked pretty fine for me.
i did have a teacher sell a book she created just for her class, but looking back the book didn't have any unique information that a regular one wouldn't have. i think she just did that to make $. i can only think of 1/3 times when a specialized book for my school was actually necessary to buy
in the event there are assignments you did not expect and you have the wrong book, ask someone can you copy the assignment either by hand or copier. i had no issue allowing bookless classmates to do this