Earlier quoted context omitted.
No. Most self-hosted services have no bandwidth costs, at all. Or they have bandwidth costs around a dollar per terabyte. Which, even when maxing your connections, would always be below your actual server costs.
If you read the fine print of the ones with "no bandwidth costs" you'll find that service becomes throttled after a certain level of usage. These are businesses, they have to make money to operate, they're not in this for charity
I’ve read the fine print, and called them.
Online, Scaleway, OVH, do not ever throttle you.
Hetzner requires you to buy traffic, but there it costs 1$ per 1TB of traffic, which is 1000x cheaper than Firebase.