From what I understand NFT's are just links to off-chain digital assets (pictures, sounds, videos and etc.). The thing that is unique about them is their on-chain address that stores the link to the off-chain digital asset. IMO, $8,400 is overcharging at a factor of least 1000X.
I would agree that they are just a modern digital flim flam money making scheme that uses the claim of them being a unique one of a kind as a smoke and mirrors trick.