For 1 percent of the 1 percent, the 737 Boeing Business Jet must be a pretty comfortable ride.

A 10-year-old BBJ at Boeing Field last Friday provided a rare glimpse inside one of the posh jets. If new, the basic Renton-built 737 airframe costs an estimated $40 million to $50 million — and luxurious custom interiors, installed by independent designers, can easily double the cost.

The jet-maker has delivered 135 of these 737BBJs since 1998. Last year, it delivered just four.

The one displayed last week, on its way to the Asian Business Aviation Conference & Exhibition in Shanghai, is being marketed by Florida charter company National Jet for about $40 million on behalf of an undisclosed owner.

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