good news about the drugstore mix, I made almost 10 gallons of the liquid stuff for ~7 bucks

if you fill up the bucket of the mac so its displacing the liquid from inside its more than enough to do a compact mac, also being much milder it also is less prone to splotching issues, but plan on spending at least 8 hours in the light, and poking / stirring it every so often

It took my mustard yellow //c to almost brand new white over 9 hours, quite happy with it