When I was a nanny, I lived on $620 a week...monthly break down:
Rent:$500
Utilities (including cable):$150
Car/Insurance:$300
Phone:$100
Student Loans:$300
With incidentals, I still felt like I was more than comfortable (and this is in Chicago).
Now that I am a grad student, my rent is up to $950 monthly and my income is closer to $2000 monthly. It's amazing what you can become comfortable living on.