To add a Unit Price item you just need to add a new line to an Unit Price section. A section can be either all Unit Price or all non-Unit Price - you can't have mixed Unit Price & non Unit Price line items in the same section.
To Add the Unit Price Item:
Select the Detail sheet. From the Paymee menu select Add -> Section. Then select on of the following sections (depending on if you want it counted as Extra Work or not):
