I bet it's more expensive than a plastic bag.

It's not rare but it's a pain in the ass to purify and transport. Semiconductor place I used to work had a gigantic 1000 gallon tank of the stuff they had to get refilled every month. Had to have some specialty chemical tanker truck it out. Then there's problems with icing your whole setup once you actually have the stuff and try to use it. It's less of an immediate fiscal strain and more of an expensive infrastructure problem.