Towelliee makes around 7-8k/month according to an AMA he did a few month ago and it has quite a bit of insight there.

He's shown that you don't have to be top gamer skill wise to make a lot of money. He's decent at games, but he isn't any sort of 'Pro' at any sort of game he plays:

http://www.reddit.com/comments/tufo9/i_am_a_twitchtv_partner...

http://www.twitch.tv/towelliee