With that I would agree. The sum of the parts will always cost you considerably more, however much you kid yourself otherwise - unless perhaps you can do the work yourself. If you buy and restore cars and pay someone to do it for you, you will get back a fraction of what you spent. The same is true of houses and boats and .. .. .. aircraft.
However, it depends on whether you are doing it for an investment.
If you want a reasonably priced aircraft in great condition you can still buy a poor one, as long as it is structurally sound, fit some up date avionics, give the airframe a respray, get the engine zero timed and end up with a really good "modern day" classic. Dont expect to ever get your money back, and if you can buy one to the same standard it will inevitably be cheaper. However, you will gain a certain satisfaction form the project and will end up with an aircraft you know is "right" (so long as you are very careful with the people you use) and that is exactly how you want it. Keep it for ten years, and it will serve you very well indeed. I speak from experience.