[jvanderbot]

Above comment said it was not scarce, not that it wasn't valuable.

[ponector]

If it is not scarce - the value is low.

[whoknowsidont]

Breathable air is pretty valuable, at least for me. And it's definitely not that scarce on this planet.

[qwytw]

Well it was. Supposedly it cost about the same as wheat by volume (and salt is ~50% more dense). So it was dirt cheap.