I'm afraid I'm in the more questions than answers category also.
Without any idea of how elaborate or "gourmet" you're breakfasts, available snacks or other refreshments are, it could be 10% on the very low end, or near 20% on the high end if you offer quite a bit of food based amenities.
Ours seems to be in the middle somewhere. We're offering a full multi-course, restaurant style breakfast, lots of baked goodies, an afternoon snack, self-serve beverages in the form of teas, coffees, lemonades, sodas, bubble waters, bottled waters in rooms, etc.
We use mostly organics, lots of local produce, quality meats, real maple syrup, etc... and the much better half and her 30+ years of restaurant/food service management experience seems to be happy with our food costs.
So, based on info you gave on the other "pissy" guest thread, there are like half a dozen owners invested in a 6 room B&B?
We are a group of 4. Our rates range from $155 - $300 p/n. We are within a 1 hour drive of Manhattan and do have a fairly high occupancy rate. Supporting? no...but supplimenting, yes.
Unless you are located in the highest occupancy market in the country and your rooms are $300 per night, how is this venture supporting the financial requirements of all those people?