This question already has an answer here:
How does pricing with AWS works.
By exemple: 1024 Go of Data Transfer Out in their calculator (http://calculator.s3.amazonaws.com/index.html) cost about 120$.
If you remove this 1024Go and move it in "Total Data Processed by all ELBs", it cost way less, about 30$.
Basically, my question is : Does you pay for transfer being sent from your EC2 to the visitor connected to the ELB? Which price is right?