You got ripped off. $8.00 is too much for a dry bag.

How much do you consider as a reasonable price for a 40-lb bag of
gypsum? You may be getting it from a farm supply store. I don't know
any farm supply store nearby. The closest farm land is
multiple-10-miles away. I can only get it from local nurseries. I
guess this means I will have to get it where I can find it.

Jay Chan