Looking for a way to get a guaranteed commission at least once a month in order to pay for wow time.

I own the game and most of the expansions (I had to stop playing before the newest) And I decided that I wanted to get back into playing it with friends again, the only problem is that I cannot currently pay for it out of pocket.

My sketches are $15, if I could just find a way to guarantee at least that $15 commission once a month I'd be set.