xmen costumes

Polyester resin/fiberglass and hard urethanes are used to create simulated metal props fairly often, but these take some getting used to.

You can sculpt positive or negative molds (preferrably both) and force a heated sheet of thermoplastic into them.

Papier mache is dirt cheap and as light a material as you'll find. The trick is to use only as much glue as you need, use small pieces of thin, absorbtive paper, and do lots of thin layers rather than a few thick ones.

I've made some metal props using liquid latex that was intrinsically colored with acrylic metallic silver paint.

All of the above materials can be painted to resemble metal.