need help looking for foam. not the soft kind

[cheapgoose]

hey guys, maybe some of you have experience in make molds for carbon fiber stuff. We're making a prototype of something big and aerodynamic. but we need some foam so we can cnc it. the foamular stuff is pretty damn expensive, and we don't really wanna use expanding foam.

any ideas> the model is about 9' x 2' x 4'

thanks

edit: not the soft kind of foam, high density stuff.