Seriouly don't make the 600 an "option". Saddling a client with one of these things is not good for ones long term employement prospects or repeat business. You can't do HI without wet foot print so it should be out anyways.
Some guys get stars in their eyes when they see how cheap a CL-600 or GII can be had for. There are a reason these airplanes are cheap! I forget to mention another reason not to buy one...when figure it out what a turkey it is the resale market tough on these old birds. Prepare to take a bath.
Challenger 300 would be a good option for you. Considering all the ownership costs I'm sure it will work out cheaper then a Challenger 600.