The trick is to wrap your technology with a service-style abstraction so you don't have to communicate all of these painful little details. Then, all of those details get rolled up into something like a quarterly report.

The terms of this relationship (contract) should be approximately along lines of "you provide us a service with a certain level of quality and in return we grant you an annual budget of $X".

At a certain point, having detailed analysis of every last expense will cost you way more money than it will save.

Not upgrading a machine affects quality of service. If they don’t trust that that’ll happen until they can feel the problem themselves, what do they have an IT team for?