There is no better GH/$ relation on the market atm.
I can see that, but KNC is predicted to add 450 Th/s of hashing power to the network (http://www.coindesk.com/a-look-inside-kncminer/). Isn't that going to make the difficulty skyrocket? A 400 Gh/s miner isn't going to make much if the total network hashing power is over 1000 times that.