Notional Charging Question

One of my past students asks..

My company is going to implement the SLA for our internal customer and I'm assigned to be the project leader. I planned to value our IT services by "Charging", not actually to charge the customer but this is a good way (from my point of view) to let customer know the "VALUE" of the IT services. I try to find the "COST" of the service and use the cost as my charge base. However, in my company (maybe for most companies), a lot of components are not dedicate for one service, for example; Several services run on the same server, several services run on the same networking...etc.

I want to ask for your help on the following;
1. Am I doing right? Using the cost as the charging base. Because I
thought the cost might be the easiest way letting customer understand
the VALUE (what we have paid) for the services.
2. Do you have any practice for the cost model for the service? or do
you have any practice for the charging?
3. Any suggestion/comment/practice for the cost? charging? SLA?


Any advice out there ?