I make cakes but someone asked me for banana bread pudding for 20 people.....Should I charge what I charge per serving size when it comes to cake or does that seem off? What would you charge?

I do many things like this. I bake higher priced desserts. I take the price of the ingredients and the container and then add on my price to make it. That depends on the complexity and the time. I own my bakery free and clear and my costs are basically the electric and insurances. All things considered, the price gets up there. Delivery is extra.