Explain AWS pricing model
Answer
It mainly works on "pay-as-you-go" meaning you pay only for what are using and when you are using it. In s3 you pay for 1. How much data you are storing 2. Making requests (PUT, POST, ...) In EC2 it's based on the purchasing option (on-demand, spot, ...), instance type, AMI type and the region used.
More on AWS pricing model here