After doing a Samurai armor in EVA foam - I'd suggest Rubbermaid.
Don't get me wrong - I love the look of my armor (here's a progress pic:
Link), but stringing all the plates together was hell. Why? because to get the "correct" look, I drilled the holes in the plates a little bit smaller than the diameter of the cord I was using. The problem with this was that I had to litterally squeeze the cord in each hole... so it took me about 30 hours of work just stringing the whole thing.
Working with "harder" and thinner material (like rubbermaid plastic) would have made this a
whole lot easier.
Again, if you didn't calculate how much cord you're going to need for your armor... I can tell you I use just a bit over 500' of cord on my armor. If you look at other pics in the photobucket album... you'll see I had the chest armor, the "pauldron", gauntlets, thigh armor and shin armor. The 500' also include the cord I use to simalute attaching the thigh armor to the chest. In the progress picture you can see I used nylon strapping to do it - but to get the right look I cut many piece of 8'' cord that I glued side by side (this alone used up about a 100').
And cost-wise, I think both material would be very similar... so if I had to do this all over again, I'd go with the "easy route" and cut up some trashcans
*EDIT*
As for the hat... I wanted to do something like that myself, but I decided to go "The Last Samurai style"
The problem I always foresaw was coming up with the correct shape (cone) with cylindrical object (bamboo sticks)... you have to find a way for the same number of sticks to cover much less area at the top of the hat than at the bottom - how can you do that with things that are the same size at the top and the bottom. Thinking about it (and seeing your progress)... I'm thinking that the only way to acheive this would be to cut some of the bamboo stick at various lengths (maybe 2 or 3 or 4 different lengths) and that you would to assemble them 1 by 1 going like this:
Longest - middle - shortest - middle - longest - middle - shortest - middle - longest - middle...
This would mean that you would have far less sticks at the top of the hat than you have at the bottom... so they would take up less space and you be able to achieve the cone shape of the hat.
However, this is just theory... I've never tried it... but design-wise - it should work.
Just my 0,02$