Quite easy for me. There are two different method but pay by usage is the better option for mmorpg players. I have only top up USD3.00 once, used it few months ago for several days during the same lag period, and still have USD2.70+ left. MMOrpg data usage is not really that much. And USD3.00 gives you like 30Gb of data quota. Unless you turn it into VPN, only WOW data usage is counted towards the usage.

You can always give it a try, it will give you USD0.07 worth of usage during trial period, which should be good for quite a few hours.