The same place you get 50 cent antibiotics and $1 DVDs. If you are in the US, UK, CA, or western europe no need to apply. The publishers have decided you can pay more and will charge you thusly.
Or try to get one of the international students to give you theirs. Makes you laugh internally to know you spent $100s of dollars on engineering textbooks while the internationally student sitting next to you has the same one in paperback and probably paid $10 for it. And that's if their government scholarship doesn't include the book stipend.
Buying international versions was one trick I wish I had learned when I was just starting college. It would have saved me a lot of money over time for the same content.
You used to be able to do so through Amazon but the publishers caught on fairly quickly. I managed to get a bio book that way, my ex-gf bought her organic chemistry books ($$$) this way as well. The next semester they were no longer visible even when searching by ISBN.
Or try to get one of the international students to give you theirs. Makes you laugh internally to know you spent $100s of dollars on engineering textbooks while the internationally student sitting next to you has the same one in paperback and probably paid $10 for it. And that's if their government scholarship doesn't include the book stipend.