Gridseed is doing 300 khs at 50-60 watts these days. They claimed 10 watts, but none of the reviews show that low power use.
Even a $200 ($230 now) R9-270 will do 450khs at 150 watts. Hardly 10-20x the power.
Just checked, my 10 Gridseed units running at about 3500 khs total in scrypt only mode doing 70 watt on the wall. It's less than 7 watt per 300 khs.
10 Gridseed miners running between 3300-3500khs (varies due to the switching pool I'm using) pulling 100watts (thats 10 miners, 1 usb hub, 1 RasPi, and 2 PSUs) in total. I've also got the frequency set to 850, so I'm sure that pulls extra watts vs the 7watts/300khs on default 600.