When you select the rate type, you can choose Create unit type.
Then you'll be prompted to fill in the blanks in:
at a rate of ___________ USD per _____________
Enter the amount in the first blank and in the second blank you'll define the unit name (for example, article or blog post or white paper or video). Once you've created a unit type, that new unit type will be an option for rate type in all future Work Orders.
If you've selected a different currency to use with this Vendor, USD will be replaced with the appropriate local currency.