Once you have the materials, it's not very expensive per unit. But a roll of carbon fiber cloth, carbon tow, epoxy, plywood for forms, molding material like Tap Plasitics Qwik Cast or similar and mold release wax or PVA release can get pricey (to say nothing of my very cool, but very cheap, home made post cure oven). The actual cost of the gear per unit is not much, but accumulating the supplies can get up there.