A turboprop is THE way to go though.
Nice thought, but I looked at the Cessna 208 some years ago. There were competitive direct operating costs bandied about but when I enquired about cost per hour for the engine, it didn't stack up. Assuming you make it trouble-free to overhaul time (which is quite likely with the PT6) you need a new 'hot' section after 3,500 hours at in excess of £100,000. This'll only really be viable if you can do Public Transport IFR in it and as we all know, the CAA are still reluctant to go there. Great pity.
Dunno about a turboprop in a PA28 - is there one small and light enough, gearbox & all? What would the total cost of ownership per hour look like, the only meaningful figure in my opinion?
Cheers,
The Odd One