C.K.
Since you only have one babe, the factors are going to be how often are you using this sitter, and what is the age and experience.
I would say for a teenager who comes once in a while, I would say $6-$8/hr. For a more someone 19+ $10/hr. If they are coming as a "nanny" on a scheduled weekly basis $12/hr.
I used to be a nanny and sitter in college in order to make rent, though at the time I lived in NYC and there was a much higher cost of living. There as a nanny I got $500/week and was on call, and as an occasional sitter I made $15-$20/hr.
So when I look at that, I drop it by 1/3 because the cost of living here is soooo much different.