There was an article that described that in UK one needs 1 megawhat-hour battery over the winter to be grid independent. Judging by current trends in few years that will be below 40K USD. While this is indeed very expensive in most of US due to much more sun available the required battery would cost below 20k. One can also have a backup generator that can run constantly at maximum efficiency to replenish the battery. Then the whole system can already be below 20K. While expensive, it provides true independence and I suspect grid cost and centralized power is more expensive for society.

These studies tend to always rely on a perfectly balanced grid without any extra capacity to find these massive seasonal differences.

Add a bit of extra capacity to the wind/solar installations and the battery figures usually plummet.