A bit of searching here will turn up some fairly detailed discussions of this in the past, I remember seeing them.
In the mean time, reserves!
Engine: 10 (of your currency) per hour
Brakes and tires 1 per hour
Vacuum pump and alternator 0.5 per hour
Avionics recert and upgrade 2 per hour
Database renewal? 1 per hour
Instrument recert 1 per hour
ELT recert? 1 per hour
Propeller (fixed) inspection/dressing/repair 1 per hour
Battery 1 per hour
So reserves set aside = 18.50 per hour would be wise, in addition to the other direct operating costs.