14,
The Challenger 300 may be a good alternative. Its the cheapest airplane with a flat floor. G3 is definitely not possible out of John Wayne and in Europe due to noise. But your aviation manager surely mentioned that?
How many hours do you currently charter a year?
And yes, rule-of-thumb, the first hour on a less-than-10y-old super midsize jet will cost you 1m, and each subsequent hour is 3000$, plus landing fees, catering, crew overnight. The 1m is your fix cost, whether the airplane flies 1h or 500h. And be cautious about things breaking down, just to give you a few examples, a flight display is 75k (and your typical jet has 4 of those), the coffee maker, DVD player, microwave is 7k, a hydraulic distribution vale is 35k.
Your aviation manager should be able to produce tables of comparison between each of the airplanes mentioned in this thread, and he should be able to guide you through the market and identify the good deals for you.