The rarest item on Roblox is the Dominus Frigidus hat. You will be astounded to know that there are only 26 copies of this item released to the store for $487.50. A Roblox user by the name Sethycakes designed this item when he visited the headquarters of Roblox as a part of the Make-A-Wish foundation. Right now, the Dominus Frigidus hat is priced between $250,000 & &7.7 million. Because of the price and the few number of copies, you can consider this item as the rarest item available on Roblox.