I also didn't buy any books for my MA courses. All of the required readings were made available in the department library to either read there, or to photocopy. I also was able to find copies of most things in the main library.
As springhaze said, I also found that it wasn't really necessary to read every single thing on the syllabus every week. It was sort of expected that you might find some of the readings more interesting than others, and really delve into those, and perhaps even read other texts on those topics that were not on the reading list. In my experience, really understanding a couple of the texts was better than skimming a bunch of them when it came to class discussions, papers and exams.