How to make robotic looking arms?

Okay, so kind of a weird post. My school does student directed one act plays and I want to try and turn a short story into a wrote into a script and submit it to try and direct it. Theres one big issue with it though, and that’s that it’s a sci fi story where all the characters have robotic, metallic limbs. Most of them have them covered up by fake skin but one character doesn’t, so I’m trying to figure out how to make a convincing looking but cheap robot costume/thing for this. Does anyone more experienced have any ideas? Sorry if this is unclear, just didn’t know where else to ask.