I agree with TexasSugar. Figure out how much your expenses are, calculate your time (pre-baking, packing up your materials to travel, travel time, set-up at your location, the class, clean-up, travel home & unpacking at home + any time spent developing special materials/ideas for the class and any follow-up), multiply time by your hourly rate and then add a little bit. This would be your minimum price for the class. Divide this by the minimum number of participants and then you have a per person cost. Be sure you are paying yourself enough and I agree, however long it takes you, remember it will take your class participants longer and just how "serious" they are about it (vs. it being a fun "Girls night out") will determine how much you can get done.
Assuming I'm providing everything and it's a 2.5 hour class, I'm thinking that a class would have to be about $200 minimum for me. If you divide that by 6 participants, then it would be about $35 per person.
One other quick thing - if you have professional liability insurance, be sure to check with your carrier about what you are covered for in this kind of instance. I'm sure good comprehensive coverage would include this kind of event, you just wouldn't want to be caught uncovered when you thought you were covered