Calling AWS ELB public DNS from AWS EC2 client How much do I get charged

I have an EC2 based client that calls this public DNS of this AWS ELB in the same region and I am trying to save money on EC2-Internet public traffic and want to keep all the data within AWS cloud. I want to know since I am calling from one AWS service to another. Does AWS services internally know how to keep this traffic within AWS ecosystem and save me internet data transfer charges? Is setting up a VPC between the EC2 client -> AWS ELB is the only way to save on public internet traffic?

Thank you