Redditor This_comment_has built this insane Hallowe'en mecha walker costume out of aircraft aluminum and sheet metal. The Reddit thread is a hilarious collection of nerdgasmic worship and internet miseryguts whining about how he made himself vulnerable to drunken douchebags who'd want to push him over.
Sheet metal, aircraft aluminum, and other parts: $600.
Rivets, bolts, hardware: $250.
Tool purchases/rentals: $200.
Truck rental to carry costume: $210
Looking like you could take down a tank: priceless.