I wish they gave a $ per KG estimate in your link about harvesting with strings. The methods detailed in this Journal article gives estimates of $2-5 per KG which is like a 5 to 12x return at current prices.

I wonder if you could couple that string method with desalination plants? Take the brine output, extract the lithium with the string method before releasing back into the ocean. Two birds one stone sorta deal. I also wonder if the string method is as technically easy to implement and separate the end products, and it's just a lot of labor if this will end up economically benefitting countries with extremely low wages. If so, that could be ecologically very bad, especially if it's possible to do with salt water brine. (As it could incentivize people to pump ocean water inland to make brine pools for harvesting).