I buy it in 25# bags from Menards for like $11. I mixed up approx. 30 cups of plaster & 15 cups water and had enough left over to do a 1/10 wing.
I may try again because the sides still ended up bowing. I am thinking of getting some Styrofoam to take up volume so its not so heavy and doesn't take as much plaster. but I need to get a new body since that one wasn't mine and I gave it back already.