We don't have a field to calculate balance due, but we can output the order total using and the amount paid. To do this in a group sales query: 

To output Order Total 
  1. Click Order in the far left column,
  2. Drag Amount from the center to Results fields to display
To output Amount Paid
  1. Explain Order in the far left column
  2. Click Sales order payment
  3. From the center column, drag Amount to Results fields to display



Optionally, this can be exported into Excel and the totals calculated there.