daycare

The average daycare in my area is 300-400 a week for an infant . I'm in school and work so that's tough. However my boyfriends cousin is 23, doesn't go to school or work and stays home all day. Can someone give me a reasonable offer on how much to pay her per week to watch my baby. The hours would vary because my boyfriend would watch her too , is 100 a week too much or too little ?