Oh my I wish those $0.10 kWh... in here we have 3 prices through the day (depends on what time it is), and the cheapest one is already higher than that :)

Anyway I did the math and it would be $7/month. More than double your estimation, but still not horrendous. Although for that range of prices one might be able to find a managed instance machine in some cloud provider...

(edit: somewhere in the process I lost track of the fact this was a price _difference_ calculation, so it's adding $7 to whatever was already the cost with a more power efficient machine, which ofc. depends on number and type of HDs and other equipment)