Besides doing a long unlock questline to be able to craft t3, you also need 2800k (2.8mil) gold in bind on pickup vendor mats to craft an entire set (+ various classic materials)
proof: https://cdn.discordapp.com/attachmen...1_21-49-08.mp4
found by the secret finding discord: WoW Secret Finding & Collections
guide: Secrets of Naxxramas - Google Docs