If you prefer to always use the cost from Service Order you can automate this functionality by asking your Administrator to enable this under the System Settings
Once this functionality is enable the Use Cost from Service Order checkbox in the Port Call drawer will be disabled and the users will no longer be able to override this.
It will still be possible to enter a total estimated port cost in the Port Call drawer or create a drafted Service Orders and update them as needed without impacting any other calculations.
Once the Service Order status is changed to Estimate, Revised or Final it will no longer be possible to do any changes of port cost directly on the Port Call