How rich do you have to be for private aviation to make sense?
That depends. How many people are you moving, on what schedule/notice, from where to where?
Once you've got more than 3-4 people going from Point A to Point B,
especially if those points are not near large commercial airports and/or the nearest airports are spokes and not hubs (so you're transferring), it starts to look fairly reasonable.
Even pounding along in a piston single, you can beat the airlines on cost and time (assuming you're instrument rated and a bit flexible on schedule to avoid really bad weather) if all 4 seats are full. For anything under about 1000 miles, 120kt will beat commercial.
Plus you can often save time if you don't live near a major airport by flying into the little town airports nearer your destinations. You can get a turboprop or light jet into basically anything with a 5000' runway.
For business travel, if you've got a group of people going, the same applies, but it's better because you can actually work on the plane.
You could be in the high 6 or low 7 figure level for a light piston or turboprop airplane, but there you’re probably doing it because you are personally a pilot and enjoy flying.
You don't need high 6 figures to fly single engine piston... mid 5 figures is fine if you're in a good flying club, and I know quite a few owners on limited budgets. You just buy what you can afford to reasonably fly, and if that's a 152, well, you know, it's still got wings!
Pistons, typically owner flown, are about as safe as motorcycles, but the risk profile is quite different, in that 3/4 of the risks are weather and fuel mismanagement. Stay out of heavy weather and keep fuel going to the engine(s) and your back near the level of private car travel.
Quite. I ride motorcycles as well, so... yeah. Lots of risk factors in my life I try to mitigate. The NTSB reports for single engine piston aviation are just a laundry list of bad decisions. "Didn't refuel because it was going to be a short flight, landing gear had problems, ran out of fuel and crashed into a forest." Pretty much anything at night with clouds - I flat out won't fly at night unless it's severe clear and most of a moon because I don't (yet) have my instrument ticket. Running out of fuel. Basic failures to fly the airplane. Kicked the tires, lit the fires, figured out the controls were wired up wrong at 100' instead of during the runup. Water in the fuel (failure to sump the tanks). Stuff like that.
Sane instrument flying, during weather your plane can handle, is pretty reasonable. And, TBH, I'm happier to be part of a good flying club than I would be to own a plane, because the engines get flown
constantly. They don't sit for weeks on end - someone or other is out flying them, and that's a great way to get reliable engines.
Anyway. </Aviation ramblings>