the "trick" is to do MS Rewards, you can earn about 15k/month in points ($15) easy just for doing literally 2 mins of stuff inside a browser plus launching a few games a week on your xbox. You can convert like 35k points into 3 months, so every 2-3 months I just add another 3 months just for using my xbox.
Since I'm still subbed out for 3 years I've been using it for other stuff, like bought the loony tunes and forza 5 controllers using my rewards money. You can join here, login/signup with your xbox email
Reward Page description!
rewards.microsoft.com
DONT turn on bing "give mode", it converts all your points into charity money