The following sample script demonstrates the use of nested CONVERTs to convert the result column into currency format:

USE Northwind

SELECT ProductName,
AveragePrice = '$'+CONVERT(varchar, CONVERT(money,AVG(od.UnitPrice*(1.00-Discount)),1)),
UnitsSold = SUM(od.Quantity)
FROM dbo.[Order Details] AS od, dbo.Products AS p, dbo.Orders AS o
WHERE od.ProductID = p.ProductID and o.OrderID = od.OrderID
AND od.UnitPrice > 8.0
GROUP BY ProductName, od.ProductID
ORDER BY ProductName