Rule of thumb would be 3-10b… as long as it remains that rare and somewhat desireable.
It is a NES skin, so there is a chance (risk?) that it will get reintroduced at some point. There is also a small risk that it will get reintroduced in a bundle. Looking at historical sales in evetycoon, we can see that there weren’t that many bought by players. The NES price was 110 PLEX for it back in 2019 (that’s 165 of ‘current PLEX’), and the last one got sold 3 years ago for 1.5b.
Note that it is not only the sell stats based rarity that matters, there is quite a lot of SKINS that are relatively rare, yet just bleak (e.g. most of old school NPC corp SKINs that were available in NES years ago). That is why some of the tournament and live event skins, which arguably are much better looking, are more desired (and expensive) than rarier, yet mundane looking SKINs.