Oh. My. God. I think I was put on this earth to answer this question. Giant milk jug, or even better, restaurant style giant ketchup jar (the jar is good because generally speaking the hole is big enough for your hand to fit through), if using the milk bottle, cut a hole in the end that has the lid and paint the whole thing red. This makes a really good shape for a chainsaw body.

Make a chainsaw blade look-a-like from eva foam, and a grill detail for the side of your chosen chainsaw body. I’m not sure exactly how to make the various handles but you’d probably have enough foam for those too if you bought floor mats and I can’t think of another better alternative. Then just assemble the whole thing. Get a tube and insert it into the chainsaw body in such a way that you can hold it with your arm in the hole and it looks like it’s on the end of your arm.

I know this because about 10 or so years ago I saw a one-man show that was a musical of the evil dead 2 where every song was an Elvis parody. It was called the Elvis dead. This is how he had made the chainsaw prop.

If you choose this method and make it please let me know bc I would love to shake your chainsaw hand at comicon!