We pay our babysitters $10 an hour for two kids (7,9) who are pretty self-sufficient and just like to play with their sitters. I prepare all meals in advance. No cleaning is expected.
Over the summer, I agreed to a $15 an hour nanny, but that is usually way out of our budget, but in a pinch was necessary.
For an infant I would think $10 an hour would be sufficient, especially since she/he would not need to cook and babies nap!