Egress is the classic shock
Data leaving the provider is billed, often at a rate far above storage. A media-heavy site can spend more moving files than storing them.
The things nobody deletes
Audit monthly for:
- Detached volumes from deleted instances
- Old snapshots on an automatic schedule
- Idle load balancers
- Over-provisioned databases
Tag everything from day one
Without tags a bill is one large number. With them it is a list of what each project costs, which is the only form anyone can act on.