I saw your site and loved it. I also wanted to be part of your costume contest. This year for 08, I custom made a costume of my own. ( keep in mind the only things not fabricated by me was the head $30 at Wal-mart and the stilts than I bought on eBay.
Attached are pics of my Optimus Prime Halloween costume along with some pics of it under construction as well as my work area and materials I used. For this costume I used about four basic materials Styrofoam, poster board, duct tape and paint, that’s about it. Oh yea, did I mention I made this from only watching the movie 3 times and a poster I got from Wal-mart.