What size cake feeds 15? According to wilton a 6 inch round feeds 12 (10 to me, I just cant get 12 reasonable servings) and a 8 inch feeds 20. Round it up. How much do you charge per serving? How much do you charge for an hour?
If you have a smart phone or tablet there are some really good apps (CakeUlator) available which can help working out cake prices. One or 2 people I know locally who have recently started up small cake businesses have found them really useful. You enter the recipe, baking time, decorating time, profit etc and the app gives you the price you should charge.
I was advised by many experienced cake makers that prices should be based on basic costs plus time and additional materials used. I worked out how much a gram of sugar, flour etc costs. How much one egg costs and so on. It takes a while to do this but it means that every time you do a cake all of your basic costs are then covered. Obviously include cost of icing per gram, basic cost of cakeboard, and what you are going to pay yourself for your time.
That should give you basic costs for each cake size and shape. Then you decide what your profit margin is to be. I know this sounds like a long process, but it will only take a couple of hours, then you have a full price list for any cake you do, unless its out of the ordinary :-)
Hi Kalaila, for cake of this size I would normally charge the UK equivalent of about $87. I would like to charge a lot more than this due to the labour intensity of cake decorating, but unfortunately this is all my market will allow me to charge, so I just have to go with it.