Super high. I'm paying around $16.50 p/h for three kids in MCOL. Also don't forget about taxes-for us its another $1200 a quarter to the state and IRS. As far as duties I would also have them do the girls laundry-I would think there would be time for the nanny to do that. Mine does the kids laundry, changes their crib sheets weekly, loads/unloads dishwasher as needed, makes them food and stuff like meatballs to freeze. She will throw in our dinner in the crock pot or oven if I ask.
ETA ignore my advice about pay and taxes..I didn't read all the responses and see you have it covered