EC2-Classic and Data-transfer

regional data transfer - in/out/between EC2 AZs or using elastic IPs or ELB means the charge for connecting somewhere inside the same Availability Zone (AZ) using a Public IP or ELB. This occurs if you choose to communicate using your Public or Elastic IP address or Elastic Load Balancer inside of the Amazon EC2 network.

• Where in our public documentation can I find special data transfer pricing for elastic IPs?

The documentation is here, https://aws.amazon.com/ec2/pricing/on-demand/#Data_Transfer

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Amazon EC2, Amazon RDS, Amazon Redshift and Amazon ElastiCache instances or Elastic Network Interfaces in the same Availability Zone

Using a public or Elastic IPv4 address $0.01 per GB

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• Datatransfer EC2-Classic -> EC2-VPC it's considered in/out/between EC2 AZs? and viceversa?

It's the same scenario with using both instances in the same VPC. If you use public or Elastic IP address for this communication(EC2-Classic -> EC2-VPC and vice versa), $0.01 per GB is charged. If you use ClassicLink and use private IP for this communication and both instances are in the same AZ, the transfer cost is free.If the instances is not in the same AZ, it costs $0.01 per GB.