Tariq Malik has a piece on the new space prize today, in which he writes:

Former astronaut and U.S. senator John Glenn’s 1998 space shuttle seat cost NASA $50 million, and private orbital passengers like Dennis Tito and Mark Shuttleworth have paid about $20 million for jaunts to the International Space Station, McCurdy added. At present, British millionaire Sir Richard Branson’s announcement of suborbital flights on his newly christened Virgin Galactic venture will cost around $190,000.

I’d be curious to know where he got the fifty-million number. There is no accepted cost for a Shuttle seat–it all depends on how one wants to do the accounting. I’m guessing that he (or whoever gave him the number) came up with an average cost for a Shuttle flight in the year that he flew (perhaps $350M, itself a contentious number, and probably low), and then divided by the number of crew.

But this is a completely arbitrary way to do it, and in fact extremely overprices it, since it values the cost of delivering a payload bay full of tons of cargo at zero.

The reality is that John Glenn’s flight cost virtually nothing, at the margin. They could have flown seat full of John Glenn, or seat empty, and the cost of the flight would have been identical, other than training costs. Unless the services of the Shuttle are “unbundled,” there’s no definitive way to put a cost on a seat.