Well a T-Prop is always going to be cheaper to operate than any jet, so that should answer that. Now the range issue really depends on how many people you're loading in a specific airframe anyways. A King-Air 200 would give you about 280KTAS, while the Be90's are only 245 at the most I think. You definately need to consider the typical passenger load, think you can put 4-6 reasonably in the Be90, the Be20 can hold 6-8 pending configuration. There's always the Piaggio that's the combination of Efficiency and Speed, at a cost of higher maintenance. Seats 8 also I believe.

I know the Europeans have a lot of different rules, so aircraft size and weight, noise, are all big issues that I think you should tap into local talent for.