What is the most expensive crown in the world?

Could you elaborate on the topic of the most expensive crown in the world? Are we referring to a physical crown adorned with precious gems and metals, or perhaps a metaphorical crown that represents a high level of achievement or status? If it's the former, are we considering historical crowns or modern creations? Additionally, what criteria are used to determine the value of a crown, such as the rarity of the materials used, the craftsmanship involved, or the historical significance attached to it? Finally, could you provide some examples of notable crowns that might be contenders for the title of the most expensive in the world?