I have owned my 355 for about 10 years and because of the little things i have done at the engine out service my future engine out services would likely be less than 10,000. This would include misc items etc. would not include engine or transmission or majors of anything. That being said my last engine out i did myself and spent close to 20 grand. If you just wanted to do the minimum that would have been 8 or less. Once you get to know your car the cost will come down. Significantly over time. That being said if the previous owner did the minimum your first one if you did everything that should be done to reduce your risk of future problems will be quite high.
I hope i said that ok.
Examples of things i did on my first engine out after roughly 5 years of ownership that i did not have to do is water pump, alternator, injectors cleaned, gold connector, hose upgrade for all hoses and probably some others i have forgot. Timed cams, checked valves and guides.
First 5 years roughly all the car cost me was Fuel and oil and a few oxygen sensors. Almost forgot replaced cats with hyperflows.
Second engine out belts injector cleaning, repaint covers. Other things that didnt need to be done but did for peace of mind was tubi headers (originals still good but prone to failure when used with stock muffler which i had done) capristo twin valve, gruppe m intake
Since that time have repaird all shocks with updated shock actuators ( due to the occasional light on)
Transmission gear was making noise replaced (probably was buggered when i bought it) new tires.
So my feeling is if a person budgeted about 15,000 per engine out and kept car 15 years the new owner would probably experience similar costs. This can change dramatically based on the previous owner and thats why i feel the cars can vary from 30 grand to 85 grand.
Many of the things i did were not required but probably will save me some of that money in the future or at lease not cause something more expensive to break in the future. The car would have run fine had i done a 6500 dollar service.