Anyone contemplating Snowball or Snowmobile needs to be aware that they always charge the per-GB price for data egress, on top of the hardware rental and shipping.
Ah damn, you're right. Looks like it's cheaper than the internet egress fee (looks like $0.02/GB versus $0.09/GB if I'm interpreting the pricing table correctly?). Azure's glacier equivalent might be worth a look in that case, since their egress is usually a lot cheaper.
The webpage says: Data transfers into Amazon S3 are free.
Egress means that cost of getting your data back from S3 someday.