Currently there is a 0.2$ fee / GH / s that will be reduced from the payouts.(
https://cex.io/maintenance )
Current price: 0.00686448 BTC = 4.309$ / GH / s
You currently mine 0.57$ at this difficult / month (without the fee current diff.:16818461371.2)
You will mine 0.56$ at the next difficult /month (without the fee next diff.: 17011343224.0 estimate)
So you will make 0.3$ / month / GH / s.
If the difficult stay at the next you still need 7.6946 month / GH / s to return it's price. Or you can sell them. When i started at cex the price / GH / s was 0.003 BTC (the half of the current) a month ago the prices was 0.007BTC. They are changing. Invest with care.