I got my metol from Adorama which sells Photographers' Formulary products. 100 gram jar I bought was 13 dollars. I see one pound jar is about $50 right now. My needs are so small compared to yours, so I do not have the price for quantity advantage. It was just convenient to buy from this source along with my other stuff.
If I do not get a definitive answer here, I am going to just mix up my powders and keep it in a jar for 6 months and see what it does. My printings are very sporadic. "Per shot" packaging may work well for me if I can get that to happen.