https://www.byteminr.com/register/5277dae5e13bf
I have cancelled a order with them and inquired on a few things and they very quick to respond. There is cheaper options but these guys are the most legit. I have a couple of friends using the 10 GH/s option.
Edit:Oh yes, they also gave GH/s increases recently to existing contracts when they lowered the prices of these, however the next batch is due to start the 11th Nov.
Sorry but its not so good as it seems, first it is only for 6 months and you can't sell back the gh/s... Although I agree that 6 months later the difficulty could be 10-20x from now on... But I will skip both this and cex....