: I've also been cutting my own disks from full sheet paper
Hey, another cheap guy! Here's a trick I picked up from a floor refinisher. Find a v-belt or other pulley about the same size as your desired disk. Sharpen one edge of a steel band long enough to go around the circumference of your pulley with a grinder. Fasten the strip on the pulley so the sharp edge will contact a flat surface before any part of the pulley. Place your paper on a flat wood surface and the cutter on the paper. Tap around the edge of the pulley to cut your sanding disc.

The floor refinisher cut his edger disks from used floor sander belts saving himself the cost of the disks. Because these disks were fastened to the edger by a center screw he had a sharpened pipe in the pulley's hub that cut the screw hole at the same time.