I found this excellent tip on /r/LifeProTips the other day: instead of purchasing the rather expensive Swiffer Refills, use a regular washcloth or rag instead. They fit, the corners tuck snugly into those creepy Swiffer sphincters on the top of your mop, and oh yeah, you’ve probably got a dozen crap washclothes and rags sitting around, just waiting for something to do.
Does it work? You betcha. Another user on reddit suggested using a microfiber cloth and Endust to replace the disposable Swiffer Dry Mop refills. I haven’t tried it so I won’t vouch for it, but the damp washcloth picked up all sorts of magical treats on my floor as you can see in the image.