6ft,
It's really a total impossibility for anyway to give you an idea of what you should charge without knowing your expenses. I'd strongly suggest compiling of list of expenses related to the portrait sessions before trying to put a price tag on your work.
Don't forget to include:
- print prices
- time spent on consultations (including phone time), the session, post-processing and retouching, taking the order, delivering prints
- camera and portrait gear (lenses, memory cards, backgrounds, props, programs, bodies, etc.) Remember that these costs need to be factored in across each session, or you are guaranteed to be losing money in the long run.
- gas mileage and wear on your vehicle if you shoot on location
- taxes, if applicable
- marketing costs (even if it's just a website and business cards)
- packaging materials for your client's finished print order
- costs for childcare while you work, if applicable
- any other related costs you can think of.

(Because I travel for portraiture quite often, I even have to consider the cost of boarding my dog!)
Without that information, there's no way to know what you'll need to charge to make an acceptable profit. Start there, THEN you'll get a much clearer idea of what your pricing should be.
- CJ