For a slightly unrelated but perhaps interesting side note, I doubt most billionaires are flying around in $5m private jets. A Gulfstream G650 runs around $66m. Roman Abramovich owns an Airbus A340-300, among other aircraft, that Wikipedia lists at $238m. $5m might get you a custom interior with a nice exterior paint scheme.

If anyone is interested, here's a link to a firm that designs custom interiors/exteriors for private jets. I believe the Airbus with "Bourkhan" written on the side is Abramovich's. http://www.pegasusdesign.mc/

Disclosure, I'm not a billionaire, I just like airplanes.