can anybody tell me what i can use for casting besides resin
i never sculpted the mold in the first place, but now the pepakura idea is goodWell, you could always try a rondo mix (fiberglass resin and bondo). You'd be looking at maybe $25 material costs.
I'm still not sure I fully understand though, is this a helmet that you own, and want to cast (if so, why are you casting it)? Is it purely a design that you're either going to copy, or come up with yourself? How do you plan on making the original, if that's what you're going to do?
Talk of casting means molding, and if you can't afford resin, have you even considered the cost of silicone? Even using silicone caulking will probably be around $30. Then your mother mold...
Try fully explaining the situation, and then I'm quite sure that someone here has done it before, and will be able to tell you exactly what they did and what they used.