It is OK to purchase GH/s from CEX.io !!!
Why ?
For training 
You will learn how real mining for Satoshi is without spending thousands of dollars and waiting on pre-orders.
You can have your GH/s instant and you can sell them back too. You can exchange your BTC and NMC right there.
You can exercise simple but essential operations like withdraw / add funds / TFA security etc.
In the end you will find the answer if mining / trading are really for you.