I have used this brown sugar recipe all of my married life. Sometimes I make it up, but usually it is mixed right into the recipe. In almost 35 years of being married, I have purchased maybe 25#s of Brown Sugar.
1 cup white sugar + 2 Tbs molasses = 1 cup brown sugar
When I make cookies calling for 1 cup each brown & white sugar, I simply put 2 cups of white sugar into the recipe and 2 Tbs of molasses. I quit measuring the molasses about 5 years into it. After a while, you will be good at measuring it too.
A bottle of molasses on your pantry shelf lasts much longer than 20#s of brown sugar.
Happy SWEET Thrifty day, Pegi