I think it really depends on a number of things.
How many children will the sitter be watching?
What, if any, chores are involved like cooking or bathing.
How long will the sitter be there?
Will the children even be awake?
Do you have to pick up/drop off the sitter?
For the easier jobs, like when the kids are already asleep (or going to bed soon) I tend to pay less. But, honestly, if I find a good sitter that I would use again I will pay well, at least $10/hr because I want her to say "yes" to us again!
Mama to Zoe (8/00), Morgan : (10/01), Brooke9/06), Casey 20wks (2/08), and Riley : (2/09)