Cex's actually rents the GH/s from some chinese miner, they pay a electricity fee and charge you a maintenance fee, that's why they shut down cloud mining. It's not profitable at this price levels, now you can see their miners are mining on chinese pools, they presumably have lower electricity costs. You will not be able to cloud-mine on cex.io until btc>350, you can continue mining with your own hardware on ghash.io thought.