I've run my Aviat Husky for over 2000 hours. The biggest variable is
maintenance. It now breaks down like this:
FIXED COSTS
Hangar 2700 per year
Annual 1000 per year
Insurance 270 per year (liablility only)
TOTAL FIXED per year 3970

HOURLY COSTS
Fuel 9 gph @ 2.55 per gallon 23 per hour
Maintenance 12 per hour
TOTAL per hour 35

So for 100 hours per year it is $75 per hour
for 200 hours per year it is $55
for 500 hours per year it would be $43

I also run floats about 100 hours per year, which I have to pay $1000
to rotate (500 each way) and the floats need mainentance of about $500
per year, so the floats run about an additional $15 per hour.

You say to leave off engine rebuilds, prop rebuilds, avionics and
airframe long term rebuild and depreciation, which are all considerable
expenses, so I did. However if you sell the plane after so many years,
those items will be captured at sale time unless you spend the money to
rebuild the aircraft and then sell it. An exhaustive analysis would
include cost of capital and tax issues as well. All of these items
probably add $20 or more to the hourly costs, and they are real costs,
but most pilots are deferring them or ignoring them.