You know with interest rates being as low as they are, it's not very hard to buy an $800,000 airplane! Put it this way, if you can put 10% down ($80,000) you can "own" a King Air for about $4,000 a month. Certainly not chicken feed, but doable if your making a reasonable amount!
The real question you need to ask them are they able to afford the $200,000 annually it takes to fly a King Air or Citation 100 hours. Those are fixed costs (i.e. hangar, insurance, pilot, maintenance, etc.) and the checks need to be written, granted the more they fly the less it costs (i.e. flying 400 hours annually costs $400,000).
I find that the cost of operation is what makes the talkers, walk!
Having said that, once your uncle's group comes to understand the cost of operating an airplane, an airplane does become an incredible tax benefit.
Then once the group gets serious have them charter a King Air 90, 200, a Citation 500, 550, 560, CJ1, CJ2. See what floats there boat.
Is there any particular reason they're also not looking at a Conquest or Lear?