The price of items on the steam market is controlled by its supply (rarity) and demand (look). If it looks good, but it isn't rare, than people will pay more than they would for something of the same rarity. If its rare, but doesn't look good, people will pay less than average. If its rare and does look good, then it will become a legend, like the Dragon Lore, any Night skin, or a fully blue Case Hardened skin.