Figure about 3 times the cost of fuel burn per hour to cover all the expenses (insurance, tie down/hanger, parts, ect... you know, fixed costs). Maybe a little less since you would be doing all the maint. and such.
Figuring an 8 gal/hr fuel burn, times 4.00/gal would be 32.00/hr, multiplied by say 2 (since you won't be paying a mechanic) = 64.00/hr operating cost. That would be "wet"... 32.00/hr for just the fixed costs.
I'd round that up to 40.00/hr just to be on the safe side.