That is up to you. You need to figure out what your time worth and go from there. I charge $75/session for 1 person and anywhere between $45-$35/session/person for groups of 4-6. I usually break it down according to the amount of time it will take me to travel to the location, the actual training time, other logistics (gas, taxes, wear and tear on my car, parking fees, etc.) and of course how much money I want to make. I give my clients a small discount depending how many sessions they buy.
Also, check to see what your competition is charging as well and then make a sound desicion.
I hope this helps. Good luck!