The first few posts in this thread pretty much nailed the point so I wasn't going to add anything. But it sort of veered off in a different direction. Owning an airplane is like owning any other 'big boy toy'. You're probably not going to make any money owning an airplane, boat, fast car, or any other hobby unless its your full-time job. It'll very rarely be cheaper than flying commercial or driving. You're paying extra for the convienience or the fun of the hobby. The costs the other posters listed are correct. If you do it right, owning an airplane will cost you about what a mortgage payment would be. Let me repeat myself - you're paying for the convenience.
The only piece of advice I could add is this: Do lots, and lots, and lots of research before you buy. And if you say, "yeah, I've done all the research".... go and do some more research. Go look on aerotrader and barnstormers and find someone selling an airplane locally. Go look at it and talk to the seller - even if it's not the airplane you want. You'll be amazed at how much you learn. Then go look at an airplane you would buy. Then walk away. Never buy the first thing you look at. With a lot of knowledge, a ton of patience, and a little luck, you'll bring home an airplane you won't have to drop a dime into for at least a year.
It's a buyers market right now and it will be for the foreseeable future. I see airplanes with great avionics packages and less than 700 TBO for cheap, and the sellers seem to keep dropping the price when it doesn't sell in 30 days.
Here are some more tips:
- Older airplanes are way cheap. A handful have less than 2000 hours on the airframe. That's basically a new old airplane.
- You don't want an airplane that was ever used as a trainer.
- If you do find an old airplane with low time, make sure it was flown regularly. Hangar queens = big $$$$ over a short amount of time.
- Damage history is okay. Most of the time damage was repaired to new or "like new" condition and it can be used as leverage in price negotiation.
- A single engine airplane with >1500 TBO is going to seem crazy cheap, but you'll pay for the $20-$25K overhaul in a few years or have to sell it for a huge loss. You're always better off paying a little more for an airplane with <1000 TBO and not having to worry about the overhaul for a long while, if ever.
- Find out what ADs are out there for the airplane. For example, if you have to pay $100 for a prop inspection every year, find an airplane with an upgraded prop without the AD. It'll save you in the long-run.
- MX logbooks. Check 'em and have an A&P check 'em.
- If you do buy, try to get a fresh annual (as opposed to a pre-buy inspection) as part of the deal. If you have to, pay half the inspection costs (but the seller should pay for any required repairs). It'll be worth the investment.
- Don't buy an airplane with fancy avionics (or think you can always upgrade, you probably can't afford it anyway). A GNS-430 and/or a panel mounted Garmin 396 is a poor man's G-1000. Similar capabilities at only a fraction of the cost.
- Yes, airplane parts are bought and sold in terms of AMU - aviation monitary unit. 1 AMU = $1K. If that's a shock, you probably can't buy an airplane. Preventative MX and smart shopping is the best prevention for airplane part sticker shock.
- Finally, build a spreadsheet to break down hourly costs and fixed costs vs hours you'll fly per year. If you fly 100 hours per year a C-172 may only cost you $120/hour which is comparable to a rental. If you only fly 50 hours per year, you might as well rent.
- If you don't plan on flying whatever it takes to get the hourly costs down, look for a fractional ownership. It's the next best thing.