Te dejo un Query tal vez te ilumina un poco el camino 
Select T0.ItemCode
,T0.ItemName
,T0.SalUnitMsr'Unidad Medida'
,sum(T0.Saldo_Inicial) 'Saldo_Inicial'
,sum(T0.Entradas) 'Entradas'
,sum(T0.Salidas) 'Salidas'
,sum(T0.Saldo_Final) 'Saldo_Final'
,sum(T0.CostoTotal) 'Costo_Total'
,'Costo_Unitario' = CASE
WHEN sum(T0.Saldo_Final) = 0
THEN 0 ELSE sum(T0.CostoTotal) / sum(T0.Saldo_Final)
END
from ( SELECT T1.[ItemCode]
,T1.[ItemName]
,T1.[SalUnitMsr]
,sum((T0.[InQty]- T0.[OutQty])) 'Saldo_Inicial'
,0 'Entradas'
,0 'Salidas'
,sum((T0.[InQty]- T0.[OutQty])) 'Saldo_Final'
,sum(T0.[TransValue]) 'CostoTotal'
,0 'CostoUnitario'
FROM [dbo].[OINM] T0 INNER JOIN [dbo].[OITM] T1 ON T0.ItemCode = T1.ItemCode
WHERE T0.[DocDate] < '[%0]'
GROUP BY T1.[ItemCode], T1.[ItemName],T1.[SalUnitMsr]
UNION ALL
SELECT T1.[ItemCode] 'Codigo'
,T1.[ItemName] 'Descripcion'
,T1.[SalUnitMsr] 'Unidad Medida'
,0 'Saldo_Inicial'
,sum(T0.[InQty]) 'Entradas'
,sum(T0.[OutQty])'Salidas'
,sum((T0.[InQty]- T0.[OutQty])) 'Saldo_Final'
,sum(T0.[TransValue]) 'CostoTotal'
, 0
FROM [dbo].[OINM] T0 INNER JOIN [dbo].[OITM] T1 ON T0.ItemCode = T1.ItemCode
WHERE T0.[DocDate] >= '[%0]' AND T0.[DocDate] <= '[%1]'
GROUP BY T1.[ItemCode], T1.[ItemName],T1.[SalUnitMsr]
) [T0]
GROUP BY T0.[ItemCode], T0.[ItemName], T0.SalUnitMsr