How does the cost and resiliency compare to purchasing energy from the grid?

For reference, I buy 100% wind source power from Xcell @ $0.14 / kWh. Reliability is generally very good, but to compare apples to apples it would cost ~$500 to purchase a backup generator [1] for the 1-2 hours of outages we have every year.

[1]: a battery system would fulfill a similar role, but I'm not sure of the cost -- and for something that I would essentially never use, it may actually be better for the environment to keep the generator.