You do avoid some of the cost, because you can direct a significant amount of your traffic over v6 and not need to CGNAT it. The failure mode for your v6 faili

You do avoid some of the cost, because you can direct a significant amount of your traffic over v6 and not need to CGNAT it. The failure mode for your v6 failing is the same as it is for v4 failing in a v4-only ISP: stuff breaks. If you want to fix that you need a redundant failover setup, which is the same thing you need in v4 except cheaper because it doesn't need to do CGNAT.