How much data? 10 TB will "only" cost $900. Alternatively there's the "ship us hard drives" option. Failing that, if you're at a crazy scale, we did announce a switch-and-save program as part of Nearline (https://cloud.google.com/storage-nearline/).
Depending on how much you're storing, the one time hit to move may make sense given our ~25% lower cost per byte (and as you mention way better GCE pricing).
How'd you arrive at that number? To my understanding, you get hit up twice -- paying for data leaving S3 and data entering GCS. The other thing to keep in mind is that if lots of your customers are also using AWS, their S3 traffic from you is free.
No, you only pay for egress (outbound traffic) not ingress. You pay for operations (GETS and PUTS) on each side but the total costs are going to be dominated by the egress.
Depending on how much you're storing, the one time hit to move may make sense given our ~25% lower cost per byte (and as you mention way better GCE pricing).