Uni textbooks tend to be very expensive. Do students really need to buy the most updated versions? Or do you just tend to borrow from the library (which would probably be hard to get if everyone could do so
)?
For example, I've got a Calculus textbook - Stewart's Calculus 4th edition but the 6th edition has been out for a while.
It really depends on the subject.
I do science and my two main areas of study are maths and physics.
With maths, at my uni you by a skeleton set of the lecture notes and they are more than useful for maths. I spent $170 on two maths text books and barely ever used them.

With physics I bought the textbook and found it was really useful because you could use it to go over anything in the lectures you couldn't fully understand.
With my breadth subject finance 1, it was very theory based and having the textbook was essential.
My advice would be to get any skeleton lecture notes for sale in the book store and stuff required for pracs, etc. If you find your lecture notes don't fully allow you to understand a certain part of the subject then I would look at buying the textbook.