Cost seems to be valid for Azure managed virtual network secured workspace as per my past experience with secured workspaces and mostly coming from virtual private network links.
You need to cross check for Own managed virtual network secured workspace from cost management tab of your AML workspace from portal.azure.com
Validation
Once we move a workspace to virtual network, Cost will include the cost of private endpoints, storage, computes, container register and online/batch endpoint
If your workspace contains premium tier container registry, key vault, cost will be much higher compared to workspace with standard tier resources.
Cost is higher for Azure Managed Secured Workspace as private endpoint are created with Customer own virtual network and Azure managed virtual network.
You can drill down the cost of your secured workspace by going to cost management tab of your workspace and selecting different metrics.
Please use pricing calculator to find the resources like key vault, container registry or storage with their respective tier type.
Hope above pointers help you validate the cost associated and find the resources incurring high cost.
Please don’t forget to Accept Answer and Yes for "was this answer helpful" wherever the information provided helps you, this can be beneficial to other community members.
Thank You.