As
@Vector pointed out, it's a lot more complicated than that. As I've been researching which plane to buy, I've learned a lot about what the costs are for these planes besides just purchase price and fuel. For example, I'm looking at a Mooney M20C that is in excellent shape. It's going for $51k, which is a pretty decent price for a plane in such good condition with brand new interior and avionics. Know what the guy paid for the last annual? Ten thousand dollars. Now, to be fair, there was a lot of extra work that had to be done last year to fix some deferred maintenance issues. But I've found in my research that most Mooney owners end up paying a bill that big at least every few years. When it comes time for a factory overhaul of the engine (about every 2-3k hours), you're dropping $35k.
Even take a much more simple airplane like a common C172. Your annual is going to cost you about $1,500-$2,000 in most places in the country. Engine overhaul is going to cost you $25k every couple thousand hours. If you want hangar space you're paying $250/mo for shared space or $350-$500 for your own T-hangar. Tie-downs are cheap at $50-$100, but a lot of people who buy their own plane don't want it kept out in the elements. Then there's the insurance. It's cheaper for me because I've got an ATP and tons of complex time, but the average private pilot gets raped on insurance premiums. Expect $1,500 for a simple C172, and it goes on up into the stratosphere for more complex planes. And then some airplanes have ADs that have to be addressed periodically. I was looking at a Grumman Tiger, and if they still have the original prop on them, they have to be inspected every 100 hours. Etc.
Realistically, owning a simple airplane like a 172 is about a $10k proposition just to fly 100 hours per year (not including loan payments). It'll cost you about $4k just to sit on the ramp doing nothing. Granted, that is less expensive than renting, but it's still awfully pricey for a middle class guy making $50k before taxes.