Do you use a budget? I mean like an actual all of your money is managed with a budget? If not, that's a good idea. You can make a category for quilt related stuff. Then you know exactly what you have available to you each month and you don't have to feel guilty if you spend some money. Make it be a cash budget- keep the cash for each category in a separate envelope- and only take that cash with you when you shop.
Also, if you know you really shouldn't be buying anything, and if you're anything like 99% of us on here, you have more projects in the works than you have time to finish any time soon! Dig one of those out and make some progress. Or, if you absolutely *have* to start something new, make a scrappy! (Come on, you know you've got plenty of scraps! ;) )I've just finished the blocks for a scrappy quilt, getting ready to sew the top together, and it was a lot of fun. I did purchase fabric for the setting blocks and backing, but will be using a brand new package of Warm and Natural batting I bought at a yard sale for $2 (score!) and will bind it with fabric from my stash, so, all in all, this quilt will have a pretty reasonable cost. If I weren't using setting blocks, it could have been even cheaper!
Anyway, my point is that not going out and buying, buying, buying doesn't have to be a drag. You can still enjoy quilting for the pure joy of quilting! :)