Cost to make would be about a plat or two. You will have to hunt Cht'k (sp?) bloodlings for a bit and get eight carapaces, put them together in a shield container from the smithing master in Shar Vahl, give it to said master to receive a large bloodling plate, put the plate, nepeta oil, and a helm mold in the forge, press combine and if your skill is fair (20ish) you will probably get the helmet. It trivials at 36, and would be very uncommon, simply because of the tedious hunting.