Want to know how much money you've made from an item?
First, add a Custom Attribute to your inventory items called 'Original Cost'. Then, add the original cost of the item as the value for this Attribute on the items you please.
Next, add your 'Gross Revenue' custom column.
Finally, move the Attribute Column 'Original Cost' and 'Gross Revenue' columns side by side so you can see how much you've made vs the original cost for the item.
Pro tip: You can also use the Date Filters to show you your Gross Revenue over a given period.