There shouldn’t be any additional fee for Kubernetes if you’re already paying for PKS. VMware may decide to charge something for the right to run k8s on their hardware but that would be in VMwares license which sounds like you’re already paying for.
For example we self deploy k8s on Vmware and have no additional license cost.
Based on what I know of PKS (haven’t looked at it in a while) it’s something like OpenShift or Rancher. Based on my experience with those and other Kubernetes service providers you’d be looking at a per node license fee.