Well I am not in a large city....but mine start at $50.00 and up, just depending on how large the family and what all you want.
I know some in large cities, are more. I'm in a small area in AR.
I actually don't charge a sitting fee, our packages run from $45-150 with a wide variety of options, such as black and white. I am in a smaller town as well. Might want to do a serch for photographers in your area. That's how we determined our pricing, by our competition.
I would also recomend that you check what the other photographers offer, like backgrounds, type of lighting, etc. Here in Guatemala most of the photographers take generic photos, with no option to get the best posibble portrait, they just say sit this or that way "look at the birdy" hehe and that's it, if you are going to give the option for your eye to find the best possible way for a person to apear in a photo, you could charge more than the other photographers.