Labor Items set up as non stock items can have a cost assigned to them. When cost budgets are entered on the project, you can select an Labor Item (non stock item). The cost assigned to this item should flow onto the Cost Budget. It should make it so the user can enter the budgeted units and the total will calculate based on the cost and units.
This will enable the project managers to budget based on units using the costs assigned to the labor items by leadership.