Ideally, salt. Deeply underground, solution mined to make large cavities. This is a preferred method for storing natural gas. Failing that, deep aquifers (not potable ones; saline water is fine).

If the basement rock is close to the surface and is crystalline, it probably involves deep mining to form cavities, which would raise the capex by maybe an order of magnitude. Other options could become cheaper then, say storing ammonia.

This is for large scale storage, of course, not for individual residences.