You get special plaster-embeded bandages that are used to make the casts for broken bones and are formulated to not produce much heat, not actual craft plaster.

I am wondering, though, if anyone had an idea of how I could calculate HOW MUCH I'd need of the bandages/paper mache. I found a good source for them both in bulk online but have no idea how I'd go about calculating the ammounts I need to maximize savings.