Interestingly, gigahash at CEX.io is now cheapest. It is at 0.00070684 BTC. After CEX.io stopping its cloud mining operation, gigahash rate has fallen. So anyone believes CEX will start operation later, may buy now.

Next comes cloudmining.website. It is still operating and paying per week. Cost is 0.001 BTC/Ghs.

Next lowest I guess is TERABOX offering 0.00118 BTC/ghs.