Not much by my account - few mil. maybe, but not 50mil by any standard. Look, from what I can gather there is no change to the product (petri dish/agar) before putting it in a heavy plastic bag and pulling a vacuum on it. In some (maybe all?) cases an inert gas is introduced into the bag to flush out the air before a vacuum is drawn and bag sealed. Heck most stores will put your fresh meat into a heavy duty bag and pull a vacuum and seal it for you. (Works great to protect from freezer burn.)
But I digress. Major players are in the business to sell lots and lots and.... lots of pre-filled dishes. They want you to have to go out and buy more dishes because your are out of date.
Look, I'm not saying it isn't a great idea, and I believe it has a place in the real world. But the big players want just the opposite. They want you to buy, buy, buy those dishes.
Just my opinion. Moo