[eesmith]

Helium is another case where the dense deposits were not found first.

Helium was first extracted as gas from rock. Wikipedia says it was first isolated from cleveite. Onnes's 1908 paper on liquefying helium says his helium came from monazite sand. https://web.archive.org/web/20180809111624/https://babel.hat...

Oh, and as a really edge case, argon gases is a renewable resource which is extracted from the air. It's cost has almost certainly gone down over time as we have improved methods for refrigeration.

(Oxygen is likely also in the same category.)