Let's take a look at some other things that are CUSTOM made for your special event:
Custom dance portrait painting. A 16"x20" portrait will be about $165.
You say, "But I'm just ordering a cake for my 3-year-old's birthday! It's not as big of a deal as a wedding!"
Well, your toddler's birthday must be pretty darn important if you're wanting a custom cake. Anything custom is going to be considered a luxury item, so if you can't afford to spend hundreds of dollars on a cake, then there's really no shame in going to the grocery store for a sheet cake.
Remember, a cake artist is making a cake JUST FOR YOU, so they'll expect to be compensated for taking time out of their lives to give your cake 100% of their attention.