The costs of aircraft are astronomical anyway!
You could buy a new 747 for about $160mil, or you could buy a 20 year old one for $5mil (or £1 from BA a few years back) and kitting it out with doors etc would surely cost less than a further $155mil...
Anyways, it does indeed look like the plan for the hold is a non-starter, however some bright-spark has already invented an alternative! The 747-8 VIP, complete with SkyLoft! It gives that extra space (taking it upto within a whiff of the size of an A380) and doesn't have to worry about cutting new doors into the fuselage. Winner.
Oh and whoever mentioned above about baggage - my plan doesn't need bags.
All I need now is $200,000,000. Anyone has this, or a 747, please, don't hesistate to contact me
I'm actually constructing a business plan to put forward to Virgin, they look like the only financially viable option.