This feature is available on all Goodshuffle Pro Plans.
Here is how to apply a discount Service to a unit/item. From your Services section of your inventory, click 'Add Service'. Then, click 'Discount Service'
Create a Flate Fee discount with the amount you would like to discount each unit.
Then, edit the inventory item you want to add the discount to and search for the discount in the Search Service text box.
Next, add the discount. If you'll always be adding a discount to this item, mark it as Required. If not, leave Required unchecked.
After you add the Inventory item to your project, you'll be able to add discount service if it's not required.
If you were to change the number of inventory items, the number of discounts would also change.