The important units are $/GH(capex), W/GH(efficiency), and $/kwh(opex).
Hit the nail on the head jimmothy.
The first two are down to your hardware supplier - kit is getting better and better power efficiency wise down to about 600W/GH from 1000W/GH last generation.
The last part is down to your hosting facility.
At Hydro66 we have plenty of spare capacity available now at prices as low as $79/kw/m including rent, connectivity etc.
A