I'm aiming for the same thing, though I'm afraid I've started working on the 3D files for Shapeways.com and Ponoko.com for the solid components (my background is in engineering so this is basically the easy part first). I haven't given as much thought as I should to the undersuit's construction. I've been looking into the cost of Neoprene sheets (as used by scuba divers) though, and it's not quite as expensive as I first thought, at $80 for a 51" x 83" sheet, a bit more than most of the black cotton clothes I see people use... but for this, I'm considering if it would be suitable for some parts, that mixed with foams.
I donno though, this'd be my first tailoring project so I'm also considering some 'duck cloth' over foam. which'd be the cheaper option.