SQL Server license from AWS Marketplace with ? cores
The market place should sell you the number of core licenses you need based on the instance size you select at purchase time.

The price will be based on a per hour or per year rate that you choose at check out. That price is just for the software license, you are still required to pay for the ec2 instance run costs as well as the EBS volume(s) attached to the instance and the data transfer costs. 

Example:AWS Marketplace

In the screenshot below the selected instance of an m4.xl for a year the sql server licenses would cost $1607 however you would still need to pay the run cost for the m4.xl at $0.864 an hour plus $0.1 per GB of provisioned EBS storage. 

If you were to assume as a simple example, you purchased the licenses for a year and ran the m4.xl on demand with an hourly rate of $0.864 and needed 100GB of EBS for the volume the cost would look:  1607 + ((720 hours per month * 12) * 0.864)+ ((0.1* 100GB) * 12 months) = $9,191.96 + (data transfer costs?)