Which vendor's selling price for Hex Nut 5 is the lowest, please give the vendor's name.
vendor's selling price refers to StandardPrice; lowest selling price = MIN(StandardPrice)
SELECT T3.Name FROM ProductVendor AS T1 INNER JOIN Product AS T2 ON T1.ProductID = T2.ProductID INNER JOIN Vendor AS T3 ON T1.BusinessEntityID = T3.BusinessEntityID WHERE T2.Name = 'Hex Nut 5' ORDER BY T1.StandardPrice LIMIT 1