You can get a reasonable idea in the near term from the announcements of CATL and BYD who are building the things.

Like CATL announced a cost of $19 per kwh. https://electrek.co/2026/07/16/catl-sodium-ion-15000-cycle-g...

which I think is far cheaper than the prices in your links. I think they'll have a job going lower for a while as the raw materials are ~$10.

I think the actual cost to buy one now it more $40-60. The $19 is probably their target in a while.

If you spread $60 over 15000 cycles that's 0.4c per kwh stored and returned which is pretty cheap compared to what I pay for electicity (~$35c).