The bandwidth is free within AWS, the ingress is also free

I've used it lately in the following setup

  - stuff on internet push their data into my bucket => this is mostly free (you only pay s3 operations)
  - on object creation, an event is fired and a lambda is spawned => this is free
  - the lambda code reads the object => this is mostly free (again, you only pay s3 operations)
  - the lambda process the data, trim it, repackage it, compress it => you pay for the compute
  - the lambda store the resulting data somewhere else and delete the s3 object => you pay the egress

=> massive cost reduction