This is easy. Wait until your preferred brand (or any brand and style if you don't care) has a sale, and load up with 14 to 30 pairs. Black Friday is a great day to wait to buy staples like underwear because you know many brands will offer steep discounts so you can load up and be set for a couple of years. After Christmas can be a good time to buy underwear as well when many merchants and brands offer sales. The point is whe you see a good sale, buy all you need plus some more.