sorry for the complete mockery and ignorance of the previous post. your question is very legitimate and many students pay alot of money for books they don't need.
As for textbooks, it completely depends on the lecturer and the class you are taking.
In engineering, i usually get course notes, and this CAN be subsidised with textbooks. sometimes the textbooks are useless and the course notes are all you need.
I had a lecturer once who wrote course notes, printed them out 2 pages/sheet, double sided and unbinded, and sold them to us for $6. then said "if you've got alot of money to spend, or you like colour pictures or you don't intend on coming to class, you can buy this $200 hardcover text book i wrote for students overseas"
on the other hand there are absolute bastard lecturers out there, who tell you buy their book so they get the royalities.
If you're not sure the lecturer doesn't tell you, it's a good idea to befriend some students in earlier years who have done the course. they will give you a better opinion of the lecturer and means to getting through the course.
Engineering is very different from business.
but the same principle applies - just ask the lecturer and older students
also, always try 2nd hand!