If chartering isn't turning out to be cost effective, then operating anything like a Jetstream or a King Air will, if the boss wouldn't want to charter it out to other customers in order to maximise his availability, be even more expensive.
Operating Costs on anything out of production, like the Jetstream, are going to be a lot higher than anything that's still being pushed off the line.
1900D are cheap, but a little bit overkill for the places you're looking at - and the performance makes some of the strips you mentioned less possible, particularly Le Mans (IIRC!)
I really can't recommend highly enough speaking to a company which already operates aircraft (I've tried PM'ing you for the advert part of this post but your mailbox is full!) - few of us will charge anything for the advice - your time is valuable, but by not involving people who truly know what they're talking about from direct, daily experience of operating aircraft you stand to lose a whole lot more.
PM me if you want the advert...!