For a 3d cake like a zombie bust. How much would you charge a customer?

A lot of factors go into that.  The first basic questions are, how much do your ingredients cost? Energy used? Extra costs? Hourly wage? Do you have a basic ‘per serving’ charge?  What kind of cake and filling?

For me personally, for a basic cake carved cake, I have made ganache the required frosting.  While I’m not sure how much a bust will feed yet, as I’m bad at figuring the cost of carved cakes, but I personally would probably have a base price of at least $100 and go up.  I’m making my husband a Deadpool bust cake for his birthday, and I plan on making everything edible, no styrofoam head, so I’ll have a better idea myself in October.

That being said, if you want it to be cheaper or easier, you could just do the chest and shoulders in cake, and a styrofoam craft head on top.