COSTS = Labor (including your own, if applicable) + Food + Utilities + Rent + Licenses + Tax reserve + Insurance + any other costs of doing business, including interest, depreciation, and all the hidden costs.
I was told one add up all the cost of your ingredients divided it by the amount. Example So you divided the serving amount by the price. So if you buy 12 eggs for 2.98. You will divided 2.98 by 12. Which would be 0.248. You round it up to the nearest hundred which would be 25 cents. So one egg cost 25 cents. If you use 4 eggs. In the cake you would have spent 1 dollar. You do that to every ingredients that you use. So once you find the cost of each ingredient you use. You then add it up and you will get the cost of the cake Or whatever you are making. If you want to factor in time you fine the hourly rate a Baker would get and calculated your hours spent making it.
That was from a friend who does catering. I know its tedious but I hope that helps.
Another thing to take into consideration with BBQ is the amount of shrinkage there is in certian meats. For instance, I smoked a brisket over the weekend, cost was $1.92 lb x 18lbs. = $34.56
I trimmed it up and came up with 5lbs of waste, smoked it and lost nearly 50% I ended up with 7.75lbs of "saleable" meat, that brisket now cost me $4.46 lb not including the cost of wood for running the smoker for 18hrs, labor, overhead, desired profit, etc.