Hi Luke, it all depends upon how much your plane is used. FTOs have the
advantage that they can fly up to say 6 times a day. So the annual and 50hour costs are spread over many flights. Also Insurance can be factored in.
If your plane's Annual costs £4000 and you only fly it for one hour a year, then it gets very costly. Some ex military Jet owners can fall into this category.
Costs such as the 50hour service (maybe £200.) can be divided by 50 to get the cost per hour, just as the cost of the engine (maybe £16000.) can be divided by about 2000 to give that cost per hour.
Fuel charges are easy, by comparison.
I think from an economics point of view, the actual cost of the airplane can almost be ignored, with interest rates being as low as they are, you might get back more than you paid for it, if you sell in ten years time.