If you want a little more unorthodox advice I'd offer, "don't buy the textbook unless either (a) it is a workbook which must be submitted for the grade or (b) you were really so powerfully impressed that you want this book as a lifelong reference." Ask the professor to ask the library to put the textbook on reserve in the library -- so that nobody in the course can take it out, but rather you share it at the library. If this leaves you muttering about Kant's categorical imperative, remember that if someone else is using it, you can form an impromptu study group and make a new friend. :D. For that matter, student societies should have copies of the texts, and a study lounge at the department might also have them. If nothing else works, copy homework problems from a friend taking the same course and look up the same material in alternative texts in the library (or on the Internet) -- but that's almost never necessary.