I mentally added up everything I've spent on my TR182 over the 15 years I've owned it, and the answer is $350-400K - a LOT of money, and that in the US where many things (e.g. fuel) are a lot cheaper than in the UK. That includes a lot of non-routine stuff: fancy new interior, new paint, two major avionics upgrades (including ADS-B), engine overhaul. The latter was $25K for the engine itself, plus another $10-15K for removing and reinstalling it.
The total also includes all the running costs: fuel, insurance, tie-down, nav data, routine annuals (not that there is such a thing in reality), and no doubt other things I've forgotten.
It's a fairly complex aircraft by "small plane" standards, but not much of the cost is due to that. I had a turbo failure which cost about $10K.