Think of it in categories -
Fixed: Loan payment - unless you buy it outright, Annual inspection, Hangar and Insurance - non of this applies to hours flown, and the annual can vary on what kind of sweat equity you or your IA allows. At a minimum this is what the plane will cost you without even taking off.
Variable costs ( consumables - per hour breakout) Fuel, Oil changes, periodic inspections, tires, brakes.
Reserves (hour based) If you are disciplined enough to set aside cash each time you fly on the happenstance that you're going to overrun TBO sometime in the next century take the cost of an engine and divide it by what you think your going to get out of your engine. I bought my F with 230 hours on the engine SMOH - at 100 hours or so per year that's about 18 years, I'm thinking the FAA will pull my medical by the time I reach 70 so...... I don't set aside a reserve - but I do have resolve to spend what it takes if I have a catastrophic failure
Ongoing - Damn that was working last week....... pretty much an unknown - stuff breaks and sometimes new or rebuilt stuff breaks sooner. Be ready to shell out 500 - 1000 without notice.
Modifications and toys - buy right - many of the older Mooneys have some nice upgrades - but if you buy right you have room to do them yourself. I bought my F in the mid 30's two years ago.