It all just depends on how much time you actually put into it. I have made over $100 a month from a single site (I have done this on more than one site) before. Now I don't have time to do much on the sites so I might not make but $10 a month from one site. Right now I'm only faithfully working just a few sites because of the time issue. I've picked a few that work really well for me and stuck with those.
Some people make enough to cover pretty much their bills. Those would be the people that work hard and get a lot of referrals.
You may have decided what to do with it by now, but if not go ahead and give it a try and see how you like it and how it works for you. Let us know!