Well, you already know of the cost issue of operation an ATF. IMO, however, the biggest issue with the operation of the 200 is the lack of spare engines for the fleet. The coast guard has most, if not all the spares. So when your plane goes in for an engine issue requiring removal, and it will, you'll likely be grounded.
In the long run, I think a late model retrofited F would be a better deal. But you're still going to be faced with maintaining a 30 + year old airframe.
Not sure of your price-point, but you can quickly get to the point where a 10 year old or slightly newer LR60 would make more sense. Unless of course it's a field length issue.