This sounds like a lot of fun!
I know a guy who worked for another building incredible props for a one-time party use(Big party, BIG money!)
They made huge blocks of foam and sculpted incredible beasties...just for this one party.
I have had people inquire if I would (for a price) hide in say, the attic of a weekend rental cottage and scare their friend wearing a costume of mine?
"Do they have a heart condition? Do they carry a gun?"
No thanks! Not enough money for that.