I just made a Buster sword from Final Fantasy with:
Cardboard (and a lot of it)
A lamp rod
So I cut out the shape of the sword and stuck the rod onto it with tape and hot glue. I next made a funky waffle pattern on it and hot glued all that together. I next hot glued another flat shape of the sword on top, covered the edges with foam, and and covered the thing in duct tape. Seem to be pretty robust but I haven't taken it to a war yet so can't be sure. I could take some pics of it if you would like.