Some of the smaller jets are pretty snug inside; a King Air might have a slightly wider and longer cabin (you have to get into the CRJ-200/Challenger 601 sized-aircraft before you get to a point where you can stand up inside.) I've flown in King Airs and similar configured in traditional passenger seating (reminded me a lot of flying Royal Hawaiian Air into the old Kaanapali Airport and LNY) and ones in exec configuration where it was one long bench seat along one side of the cabin flying sideways; the latter was pretty nice. I also suspect a jet is going to be more expensive than a turboprop, all other things being equal.