I allow myself X number of dollars a month for "quilt stuff". When I reach that, nothing till the next month. Usually have $$ left over and that goes into a stash for when I go to a large quilt show where vendors abound and temptation reins. Last year when I went to Des Moines AQS show I had over $400 in my "mad money". Must admit I put a healthy dent in it at the show, but oh my, what fun I have had with the things I bought.
I also throw change into a jar each time I shop, amazing how much that adds up in a years time.