Hourly Rate For A Sitter?

I've been craving a date night with my husband and it seems like since we had our third child a date night has become a complete thing of the past. We moved to NC from NY about three years ago which means no extended family around and no free babysitting :( I do have wonderful friends that have offered and in fact have taken my kids for a few hours so we can go out to dinner and whatnot but I feel terrible asking them to often as they have two children of their own and I'd be asking them to watch more than they have themselves, so I went on a hunt for a teenage babysitter. To my surprise I found the most wonderful girl who was fantastic w/ my daughters and managed to juggle getting all three down for bed. I had her sit for me one night so my husband and I could go out to dinner and a comedy club w/ my in laws when they were down visiting. We were gone about 4 hours total and when we returned my mother in law, after insisting, paid her $40 ($10 per hour). The short of the long is that now i'm afraid to call her back to sit because I can't afford the $10 an hour rate that she was paid last time, don't get me wrong she was a fabulous sitter and deserves every penny but if I pay her $10 an hour then I might as well sit home because I can't afford to do anything else. I'm not sure what the going rate is these days for an occasional sitter, am I being to cheap or is $10 an hour really the going rate?