Why River Reed Salt Is So Expensive

On day one, harvesters cut out these river reeds. And in eight days, after drying, burning and filtering, the reeds will produce one of the most expensive salts in the world. Just one tablespoon of river reed salt costs about $1 in Kenya. Compare that to the 4 cents it costs locals for the same amount of sea salt. So how do producers make salt from river reeds? And why is it so expensive?