There are some textbooks that have been created by other universities or individuals that can be used for free. These might not be used in your classes at AUP. It is a great deal of work to change the entire outline of a class to a new text. Some of the open access textbooks may not have all of the information that your professor wants to use. Nevertheless, these may be useful as outside references or reading if you need more information on a topic or want to have more examples, questions, etc.