As a matter of fact this is why new EC2 instances don't get swap -- running into swap can cost a pretty penny.
You can swap to local (ephemeral storage) at no charge. Or you can created a provisioned IOPS EBS volume and swap all you'd like. There's no separate I/O charge for these volumes.
I assume this is a reference to the charge per 1M I/O requests on EBS.
As a matter of fact this is why new EC2 instances don't get swap -- running into swap can cost a pretty penny.