He wanted to go as a Predator and I couldn't find anything so I had to make it. $30 later for some Cardboard and Metallic paint and 7 hours of my time and we have this! I've done it up a little more since these photos and he seems to be happy with it. My wife made the hair!
He has the Mask, Shoulder Cannon and retractable blades. Hope the teachers don't mind

Man I really wish I could push and pull vertices on a cardboard model.
Cheers
Paul