Sometimes professors will give you an option between different editions or a set of course materials that can either be bought as a package or individually. Anytime course materials are listed as "Choose" , "Either/Or" or "Part of Set" or "Pick One" - if you are at all in doubt which book is best, you should contact your professor and understand what they recommend.

Packaged materials are typically far more expensive than individual textbooks - a bookstore may be able to sell packaged materials for cheaper than they can sell individual textbooks for, but individual textbooks are typically much cheaper online because so many people are buying and selling them (it's much more rare to see very specific packages bought and sold online).