Some months I don't spend anything!
I'm fairly new to quilting, it's been two years just this past november.
I can only purchase what I need for my classes. I started quilting with a beginner class in Nov 2009 and then in January I signed up for 3 classes over the winter session. Then in the fall, 3 more. And so on, and so on (just this past saturday signed up for 3 more for the winter 2011 season).
So I buy what's required for the classes and as fat quarters are only $4.75 I'll usually buy 3 or 4 once in a while, that go together, to try to build up my stash.