You should start by reviewing historical spending and performance against expectations.
The simplest approach requires you to know a headcount: how many people do you have, or need, or are allowed to have. (This could be direct employees or temporary employees in the form of service contracts.)
To do this accurately you must forecast work requirements somehow. So you’ll need to know about the weekly, monthly, and annual planned work, plus an average rate of surprise work.
Then add factors for material, overtime, and overhead. Like material 1:1, overtime 10% or whatever history supports, and the payroll costs for en employee, or contract management costs.
At first don’t include major, irregular repairs.
---------------------------------
Karl Burnett
General Electric
Anderson SC
---------------------------------