Compared to things like lithium-ion batteries or even the lead used in lead-acid batteries, I bet it's dirt cheap.
I'd say it's the manufacturing costs that will be the unanswered question.
Can't you just pour liquid concrete into moulds, and wait a few weeks? Maybe I've just been in South East Asia too long, but there seem to be few problems where pouring large quantities of concrete isn't considered the go-to solution.
Depends the point of view. Cement production consumes a lot of energy...