Cardboard, foam board, and craft foam can work pretty well. I actually owned the D3 when I was younger! It's really small though, so you might want to try to make your own anyway.
I'd do the basic shape out of cardboard/foam board, then detail it a bit with thinner cardboard.
Use some kind of putty on the edges and where the pieces join, and sand smooth.
Detail a bit more, prime, and paint. Should be pretty basic. ;D
So have a few cosplays I want to do, but no idea when/if I will get to them.
In the mean time, I started up my website for my props, cosplay, and useful stuff. Please check it out