Eu acho que deveria ser
select convert(varchar(10),StandardCost) +'S' from DimProduct where ProductKey = 212
ou
select cast(StandardCost as varchar(10)) + 'S' from DimProduct where ProductKey = 212
select convert(varchar(10),StandardCost) +'S' from DimProduct where ProductKey = 212
select cast(StandardCost as varchar(10)) + 'S' from DimProduct where ProductKey = 212