There so many elements that go into creating your custom cake, the ingredients being only a small part of that but lets start there.
In a standard 3-tier cake which serves 120-150 people, there can be as many as a dozen eggs, 5 pounds of pastry flour, half a cup of real vanilla, several pounds of unsalted butter, several bars of premium chocolate, large quantities of fresh fruit or nuts and more! The filling and buttercream may contain 3 or 4 more pounds of unsalted butter, another dozen or more egg whites, and several pounds of sugar plus the chocolate or fruit to flavor it. If you have a fondant covering, add about 5-8 more pounds of sugar and butter.
Now you need equipment. While some of the basics are in nearly every kitchen, not many home bakers have a set of tiered cake pans in various sizes ranging from 6” to 18” (depending on your cake) and an oven that will fit the larger pans, a heavy-duty stand mixer, professional grade food colors and dusts, piping bags with specialty tips, a rolling pin that can roll out a 2 foot diameter circle of fondant, cutters, molds and more. Depending on the design of your cake, there can be hundreds of dollars of specialized tools and molds required. It’s not hard for any baker to spend many thousands of dollars on tools and equipment for their art. There are boards and boxes to safely deliver your cake and a vehicle large enough to securely transport your masterpiece.
In addition, there is the cake artist’s time to bake and create your masterpiece, her (or his) experience, and potentially thousands of dollars and countless hours in workshops, training courses, and conferences spent honing her craft.
You are paying for her baking experience in using recipes that are tasty but can stand up under the weight of being stacked and shaped, structural engineering of the support systems (that need to be there whether your cake is pillared or not), artistry in decorating, sculpting skills in creating a topper or flowers (some flowers can take up to 4 hours each to create), expert delivery and repairs of any mishaps that may happen along the way, and more.
A note about delivery: one of the most risky “cost-saving” ideas I’ve seen is to decline to pay for your cake artist to deliver your cake. She knows how to transport it safely and how to repair any minor damage that may occur. If your cake is pillared, or more than 3 tiers high, delivery is essential, but even for smaller cakes, it can be critical.
Consider also that even the simplest cakes usually take 8-10 hours of time and that more elaborate or difficult designs can take 45+ hours, it’s a wonder that a custom cake isn’t much more expensive. If it were marked up in the same manner as a wedding gown or some of the other services you purchase for your wedding/event, it would be!
Just a thought... If you gathered twenty or twenty-five of your closest friends and family, took them all out to a fancy, first-class restaurant for a special dinner ~ would you expect to pay any less than $3-$6 per serving for a special dessert?