Hello Toliver,
In standard SAP CO this is called Actual Price Calculation, transaction KSII. The Cost Center linked with the Work Center that is used in the internal NWA has a fixed monthly cost of $2,000.
In KP26 you will have the planned rate for the activity type that is maybe $40 per H, either introduced manually or calculated based on primary planned cost.
And period-end you run Price calculation that will be in this trivial case Total Cost/Total Hours and the cost will be revaluated accordingly. Depending on customizing it can either revalue original line items or post adjustments.
BR,
Paulo