[jws]

Aluminum is 1000 times more abundant in seawater than (edit)uranium. Lithium is about 60 times as abundant. With uranium at $32/lb, aluminum at $0.75/lb and lithium at $6/lb it seems that aluminum and lithium would reach commercial viability first.

Magnesium has already made it with significant production coming from seawater.

[AnimalMuppet]

I don't think your first sentence says what you think it does...

[Metacelsus]

The price of aluminum reflects the price of the energy needed to reduce it to the metallic form. Extracting from seawater would still need to pay this price.