It more or less depends on how old the child is.
I would say newborn to 3 is about $150 a week, or $25 - $30 per day.
4 to about 12 is about $20 a day or $100 per week.
I think it should be less if that person doesn't take them places, however I think there should be $20 you give them just for the child for the week, say if the baby sitter takes them to the dollar store or out to do something.
If they want any more that that, I would find someone else or take them to a daycare for the same price is not a bit less.