If you recover the methanol from the bio after settling out the glycerol you use 1% per pound of bio, 2% if you don’t recover.
I've been using 7lbs per gallon bio for calculations, so if you remove the methanol you would use 2.8 lbs per 40 gal of bio. I just use 3 lb per 40 gal.
So a 45 lb will do around 15 batches. If my math is right that comes out to a little over 5 cents per gallon.