I have been asked for a quote on a Wii-shaped cake, which is to be just a a showpiece, along with either sheet cakes or cupcakes for 90 people. I've decided to do the Wii in RKT. It's a simple shape in terms of the actual sculpting, and minimal materials to make RKT, so I'm trying to decide how to price. Would you charge as much as if you were using actual cake? I normally just quote roughly 3X my cost, but for a sculpted piece that doesn't work as well due to the extra time involved... TIA for any words of wisdom!

I price my cakes similar. There is sometimes PITA charge or I count 4x my cost if difficult design. I decided it is enough for quick pricing.

In this case - calculate from actual cake. What you could subtract is the difference in cost between cake and RKT.
The main cost is your work and time, this doesn't change.