You can download objects from S3 from EC2 without traversing the public internet using things like gateway endpoints [0] which avoids s3 egress fees. But doesn't avoid egress fees from EC2 to the end user.

[0] https://docs.aws.amazon.com/vpc/latest/privatelink/vpc-endpo...

they are indeed egregious, like, downloading all your data one time costs about three times as much as buying disks to store it.

This all depends on the cloud you are building on and if the data ever leaves the datacenter.