But unfortunately nodays with the prices of IPv4s it's like it's broken. The best price you can lease is probably in the ballpark of around 0.5 USD / IP.
I love the idea of v6, but the reality is still not worth it for most situations even at that price. IP v6 implementations are still all too commonly buggy and inconstant, and that’s on top of all the work required to bring v6 online.
There are certain auction platforms, I sold my IPs through https://auctions.ipv4.global/ which went smoothly. The registries have waiting lists for resources that get handed back to them (very rare). You need to be a member to buy IP space though.