I paid about $5 for a half-gallon. I guess you can economise by optimizing space but I’m only doing this once - now doing it for all five of my masks.
It's not so much about the money. It's more about being able to do more masks at the same time with the supply I have on hand (which was a pain in the butt to find, in our current Corona climate). 1 at a time, for a week, will take me forever. At least I can complete it in 1/2 of forever...