A wise precaution would be to allow 10 - 15% of the initial purchase price to over the first year, to get your new plane upto scratch. After that, the fixed costs are: Insurance £1-2k depending on type/cover etc. Parking £400 - £2k, Annual £1-2k
assuming no unforseen gremlins.
I bought a Piper Arrow 18 months ago. The first annual cost me £10k. needless to say it was rather a shock, but I just sold the plane and got all the money back, so not so bad after all.
If you are owning on your own...sure it doesnt make good economic sense, but what everyone else has failed to point out, is the satisfaction and pride of ownership, and just being able to turn up and fly whenever you feel like it.