National average was up to around 12c / kwh I think last time I checked.
6.4 is fairly cheap, but more than double the cheapest (Douglas and Chelan counties in Washington state are right at or a hair under 3c/kwh for residential/SMALL business rates, lower for big business/industrial. Grant county next door is 4.5c residential/small business but a hair CHEAPER than Chelan/Douglas for large business/industrial - this may change next year, as all 3 PUDs adjust rates).
Avalon 741 is pretty efficient, just not THE most efficient - and as others have pointed out, the price to pay for S9 efficiency is relative instability and a HIGH failure rate.