It's the second lightest natural isotope of mercury, comprising about 10% of natural mercury:

https://en.wikipedia.org/wiki/Isotopes_of_mercury

Since mercury forms vapor so easily, it should be easily enriched in gas centrifuges like uranium (more easily, actually, since the starting isotopic abundance is higher and the chemistry is simpler). The high price of purified mercury-198 at present is probably due to it being a scientific curiosity with no industrial demand.