I agree with all of the advice offered above.
Running costs will vary, but some factors that should be taken into account include: insurance (public liability is relatively cheap, hull and passenger insurance are expensive); monthly storage costs; maintenance (including, but certainly not limited to, the cost of the annual inspection); fuel and oil; appreciation/depreciation; reserves for engine overhaul, prop overhaul, exterior overhaul (cost of repainting), interior overhaul (cost of reupholstering), and instrument overhaul (upgrading, etc.); financing costs (or loss of return on capital, if you pay cash); annual taxes and miscellaneous government fees; annual subscriptions (charts, approach plates, GPS database, etc.). And the list goes on!
Here are some weblinks that might be of some help:
(1)
Aviation Consumer (reports on various aircraft and engine types, etc. Lots of good stuff; although you do have to purchase a paid subscription to access the site, it is probably worth it);
(2)
Aircraft Ownership Center (I have not personally used the services offered by this site, so I don't know how useful they might be);
(3)
"Skyhawk vs. Cherokee" (a comparison article by Budd Davisson);
(4)
"Used Airplanes: buyer, be cynical" (a generally useful discussion of various issues; American perspective, but still generally useful);
(5)
"How Much Will it Cost to Fly?" (extract from
How to Buy a Used Aircraft Without Taking a Dive;
(6)
"Cheap to Keep" (there's no such thing as a cheap airplane: a better title would have been "Airplanes that are less ruinously expensive than most");
(7)
"Choosing What Aircraft to Buy" (some good advice here).
Even if your ultimate intention is to have your own airplane, it would be worth considering a partnership / syndicate. That way, you will gain insight into the costs (monetary and otherwise) of aircraft ownership, but you will not have such a large financial exposure and you will have other people with whom to share the various chores. If things go badly, you can sell out at a loss, or even walk away: options that would be prohibitively expensive if you have a 100% interest.