PV can scale down pretty far, yeah, but it can also scale up. Having guys crawl around on rooftops trying not to damage your shingles is a lot more expensive than just setting up some panels in a field. The majority of PV getting installed is utility-scale, not household-scale, so you can buy cheap PV energy and live half a block from a supermarket and half a block from a chichi cafe.
As for costs, there's been concern for more than a decade about the "utility death spiral" scenario: some users disconnecting from a grid would spread the fixed costs of things like transmission and black start over a smaller number of remaining users, leading more of them to disconnect, and so on. So far it hasn't materialized anywhere, but as far as I know it could. I don't think the same scenario is likely with "legacy energy" like gasoline and natural gas, because the fixed costs are so low.
As for costs, there's been concern for more than a decade about the "utility death spiral" scenario: some users disconnecting from a grid would spread the fixed costs of things like transmission and black start over a smaller number of remaining users, leading more of them to disconnect, and so on. So far it hasn't materialized anywhere, but as far as I know it could. I don't think the same scenario is likely with "legacy energy" like gasoline and natural gas, because the fixed costs are so low.