Do you know a lot of college text book have price below 10 US$ ?
VERY, SO, REALLY, cheap
The price of international book is too high for Indonesia people. It would be impossible to afford such high price book. So, instead buy from publisher they photocopy/duplicate the book. There are many photocopy vendors which provide service to duplicate the book.
Photocopy vendors have highly developed technique for duplicate books. They can duplicate book with very similar from the real book. There are many option of duplication book which offered by vendors. The option for example, we want soft cover, hard cover, or no cover. Sometime, I think, for some vendors the duplication book is better than the real book.