I was just reviewing the EC2 hibernation video and it didn’t mention whether hibernated instances or stopped instances are charged/billed.
You’re not charged for instance usage for a hibernated instance when it is in the stopped state. You are charged for instance usage while the instance is in the stopping state, when the contents of the RAM are transferred to the EBS root volume. (This is different from when you stop an instance without hibernating it.) You’re not charged for data transfer. However, you are charged for storage of any EBS volumes, including storage for the RAM contents.