Caution is required when quoting APU maintenance costs. Maintenance costs are very dependent on the particular lease/purchase agreement for the APU.
Many APU maintenance cost structures are not cycle dependent, only hour dependent. Further, the hour costing formula is usually a percentage function of airframe hours. This is because many airframes have poor or non-existent APU use tracking systems.
If you are trying to calculate actual APU operating costs, you need a great deal of detailed airline/aircraft specific information to be accurate.
The costs for one airline operating the same APU can be dramatically different than the same APU operated at another airline.