We should not forget the principle of "charge what the traffic will
bear". $30 for a gallon of mineral spirits at an art store, or $10 at
home despot. $20 for acryllic medium at an art store, or a little
Elmer's Glue and water....you don't always get what you pay for, or pay
for what you get )

I can spend $15 for a tube (little more than one ounce) of moderately
priced "artist" oil color, which has far less of anything in it than a
gallon of "cheap" paint from wally's.

I once found a website for a company that sells all the stuff for
compounding your own paint, and there are still decorators who do that.
Wish I could find it now.