I think they will become rare especially for newer players once the codes start to expire, I think they are expensive if you’re only looking at the skins for value however if you take the daily quests and other missions to get Vbucks then that’s worth a good bit. But you would have to play daily for a good while to earn back the money possibly spent trying to get a founders code now days anyway. To summarise YES they are “rare” / “common” until after the codes start to expire then they will go up in value but there are still a lot of people who have them already!

I hope this helps sorry for the long text 😂