How much will ingredients cost you, how many hours do you estimate you will spend on the entire order, and how much do you spend on overhead costs (licensing, insurance, utilities, etc.) on a per-order basis?
I would price it as a tiered cake, not a 3D cake. It's not really a 3D. I am assuming you are using a rectangular cake for the first tier and a square tier for the second tier, so that would be tier for me.
I'd just do tiered as well. . . it's not a super complicated cake to call it a real 3D cake
I am doing one very similarly. I priced based on the number of servings and the intricacies of gaining true gold versus yellow, coloring the other book with royal blue and I have to recreate a honor society key logo.
Take into consideration any specialty you have to add to a basic rectangle and square cake.
Extra for decor, yes, but for the basic part of the pricing just a tiered cake.