If you have a router (seen you asking about bits in another thread) just by a jasper jig for the router and you can cut all the holes you need with the router. I cut 24mm all way up to 6". I have make centering rings as large as 16" dia and only use one tool. I have 2 size bits for my router 7/32" and 1/4" and can cut holes that require little to no sanding.
Yes, you can buy Gator Grit, and other sandpapers cheaper at your local store. But cheap is exactly what it is, which means in the long run you'll spend more and waste a lot of time swapping out worn out sandpaper.
I won't waste my time (or energy) with any sandpaper other than 3M or Klingspor.