Just for your reference, I googled nanny services in Chicago and this is what one of them (http://www.allbestnannies.com/index.html)
wrote on their webpage:
What can you expect to pay a nanny? In the Chicagoland area, nannies salaries are between $11.00 an hour up to $20.00 an hour. On average an experienced nanny with excellent references will earn a minimum of $12.00 -$14.00 an hour.
Higher salaries indicate formal child care education, nanny training, a degree, and/or long term employment history.
Live in nannies usually earn $500 to $800 per week. The average nanny works between 40 and 55 hours per week.