Ya agreed about that cost for a backup install - there are some interesting new options that should be less labor from an electrician.
With the 120VAC unit, about all I could power in my house is lights, TV's, and maybe some small kitchen appliances, which limits how much power I could shift off of peak, maybe a KWh or two, which makes it harder to get any payback on the investment.
Unless the spread between peak/offpeak power prices becomes larger, I'm not sure that battery storage is going to be a worthwhile investment (for me). Or maybe if the utility bought back power at a reasonable rate during peak periods as the other poster's power company does...But the California PUC doesn't seem to be interested in incentivizing that model.