I havenât looked at the following much myself, 
, but you might find that WAL archiving to Tigris strikes a better cost balance:
https://community.fly.io/t/fresh-produce-enhanced-wal-archiving-and-remote-restores/20827
At a glance, I donât see any mention of an HA cluster being a requirementâalthough there is an extra RAM threshold.
In general, volume snapshots shouldnât be considered the main backup strategy, but rather more of a safety netâŚ