A few years ago I was offered a 727 vip with aux tanks, having cross-Atlantic range for something like 4m. Aircraft had a reasonable engines and interior was refurbished for 6m just 2 years before that. Sounds like a deal? Definately not - I would not be surprised if that aircraft is still on sale. Running costs are just too high, crew and maintenance are not so easy to get etc. G3 you are almost guaranteed to be the last owner - there is no aftermarket. G4 could work but 500k a year running cost - forget about it, you will be there with just crew and maintenance (if you lucky and no hickups), hangarage, fuel, other DOCs will be on top