Please list all the vendors' usual selling prices of the product Hex Nut 5.
vendor's selling price refers to StandardPrice
SELECT T1.StandardPrice FROM ProductVendor AS T1 INNER JOIN Product AS T2 ON T1.ProductID = T2.ProductID WHERE T2.Name = 'Hex Nut 5' GROUP BY T1.StandardPrice ORDER BY COUNT(T1.StandardPrice) DESC LIMIT 1