You have a 10TiB gp2 EBS volume in the Ireland region costing $1,100/month.
The disk is heavily used at the weekend as it is a central storage location for backups. During the week the disk has no usage.
You have ten web servers in your Development environment in the Ireland region. Each server has two gp2 EBS volumes (8GiB and 30GiB). The cost of the EBS volumes is $41.80/month
The servers have a very small workload.
During the week after a period of low usage the EBS volume will automatically be modified to type sc1.
As the worload does not warrant a gp2 volumes, the system automatically changes the type to standard.
At the weekend when the load increases, the EBS volume will automatically be modified back to gp2.
Whilst the EBS volume was at type sc1, this would have been costing you $280/month, a saving of 74.54%
Unless the workload changes, the system would keep these volumes at type standard costing $23.76/month. A saving of 43.16%