Valve seat stones sizes?

I was just down at the shop and my son was using one. He is constantly redressing them on a dresser. If you get a seat grinder

Prices of his system are
Qwik-way is what they still sell as a kit, Grinder, Dresser, 12 pilots , 2 stone holders, 20 stones $4000.00 And that's the cheap dresser.

One stone is. $15 each new depending on the stone.. The pilots are what is expensive Pilots are $60 ea. That is qwik-way or Goodson

heavy duty dresser is. $1300