We charge "production fee" which is a percentage of the total cost. Percentage varies depending on the type of the project.
Right now, we are manually calculating the % and using the field for "shipping". For the label, we just changed it in the template.
Is there a better way that I don't know? If not, please consider adding the feature which we can add positive percentage (like we can add negative percentage now for discounts). Thank you for your assistance!