When I bought my TB20 in 2002, I worked out that a TBM700 cost the same £ per mile as the TB20, in cruise fuel burn.
Sadly that hides a huge vast massive difference in the diameter of the (French) barrel which a TBM owner is bent over, compared with the diameter of the barrel which a TB20 owner is bent over.
Reminds me of that old joke about the barrel with the hole in it, on a ship...
In aviation ownership, happiness is inversely proportional to the diameter of the barrel.
A turbine is a pretty bad barrel, no matter what it is mounted in. At the TB20 level of playing, you have to always be able to write a cheque for say £30k if something goes badly wrong. Obviously you hope you never have to, but that is the kind of capability you need. At the turbine level, the cheque writing capability is £300k. The dealer can dress this up any way he likes, into (not unimpressive) low costs per mile, mission capability, etc but ...
The other barrel is a highly integrated glass cockpit, but you get that in a C172 these days
Anything goes wrong, it's a flight+hotel job at the nearest Garmin dealer.
Now combine these two great advances in aviation, and you are talking big money as soon as something is not right.
Obviously if you had £10M before you started this, it's not an issue.