ITIL cost model example with calculation

I was just wondering if anyone had implemented a problem cost model. I am struggling to develop something that I think is fair given that elements could be subjective. I was asked to look at a way of calculating the cost of incidents caused due to failed changes. For example the charge to the customer based on delivery you make, per incident based on complexity or per hour for change requests. I hope somebody here can give me ITIL cost model example for this. Has anyone ever done similar to this and share experience on how you calculated this? Give me some tips or ITIL cost model example on methods that have worked. Many thanks.
