First of all, let me spill some tea. You don't need every book your professors recommend. Now, I'm not trying to set you up for failure but that's one of the key things I've learned in my four years of college.
One mistake I made as a freshman AND sophomore was buying every single book on the syllabus before classes even started. I like to be ahead and I like to be prepared, so that's one of the things I thought would set me up for success.
However, 98% of your classmates aren't going to order the book beforehand, so assignments will be postponed a little, more than likely while the professor allows your peers time to get their book. All of this to say, just wait that time and figure out what you REALLY need.
On day one your professor is going to go over the syllabus and tell you what you need. They'll also tell you what's mandatory and what's optional. I never buy the optional material for the simple fact that someone else in the class will buy it and I can meet up with them to read. Take a photo of the extra reading. Etc.
So now that you know what you need, here is where I would recommend getting them. Any campusconnect codes, or McGraw Hill online programs you'll have to get directly from the source or your campus book store. There's really no way of saving money or getting around this. :(
For hardcopy books or MY FAV, e-books, I always check Amazon or Chegg. These are the two places where they're going to be the cheapest. The easiest way to find your book is to find out the ISBN# for the book- your prof will usually provide it, then plug that number into the search bar on both Chegg and Amazon.
When an e-book is an option, I always opt for it. For one, you can look up the answers easier- think smarter not harder & don't tell your momma I told you and two you can print out copies of the book if you like having a hard copy, so in that case, you have access to both.
Anyways, check Chegg, check Amazon, last resort your bookstore. The college bookstore is almost always more expensive.