First you need to determine exactly what it will cost to make the cake: ingredients, electricity, etc, gas to go to store, cardboard cake boards, boxes for delivery, and every little item involved in the process.
Examples of costs we tend to forget:
*Will you need to purchase tools, pans, etc for the job? If so, will you use them again? If yes, then you can amortorize the purchase price over several cakes, if no, then the cost goes onto this project.
*Will you need...