There's no way anybody is going to tell you anything useful about YOUR price.
YOU need to take into account how long it will take YOU to do this decoration as well as YOUR costs.
If you have never done this before, practise your method before the actual cake.
You can either purchase the Cake Boss software or something similar to figure out your actual cost, and then do your own research as far as what others in your area charge for similar work. I hope you post this once you create it - that's a lovely cake.