I highly doubt anyone in the hobby will use more than 20 plugs/discs in a given year. Maybe if they are in the business of selling frags or something, then yes. I'm still building up my tank, and I have used maybe 5 discs from frags that I bought.
Does it work for your school project if you broke it down to 0-5, 5-10, 10-15, 15-20, and greater than 20? You may get a better spread.