Both Michael's and a store up here in NE Ohio called Pat Cataan's have been absolute lifesavers in terms of buying all my supplies, for both WWG projects and school. Unfortunately, Michael's stores are dropping like flies up here, it seems... I was able to hit one during a store-closing sale, and got some good deals picking through the remnants...
....Something worth mentioning is that many of these stores have membership discounts, where you pay a fee and receive an additional discount on your purchases. If, like myself, you find yourself rubbing shoulders with floral designers and scrapbookers in these places on a weekly basis, it is absolutely worth it. Glues, cardstock, foamcore from 22x28 to 40x60, cutting mats, blades, burnishers, acetate, just about anything you need, way cheaper than the office supply big-boxes...

Another good one is Jo-Anns Fabrics... I do a huge amount of scratch builds for my various star ship games, and I get tons of stuff from there.

John