> The relay isn’t open-source either and I’m not aware of any independent ones running; at minimum it would be very expensive to do so.

https://github.com/bluesky-social/indigo/tree/main/cmd/bigsk...

> These are some informal notes on setting up a full-network atproto Relay, using the bigsky relay software developed by Bluesky. This is the same software we run ourselves at https://bsky.network.

https://whtwnd.com/bnewbold.net/3kwzl7tye6u2y

The post goes a bit into costs as well.