This sounds comparison is pretty accurate. Since the Hellas are dual tone, they are louder and grab your attention more. They seem a lot louder through the cab too. They'll definitely draw more attention than the stock.
I got mine from Pep Boys, so it cost me $60, but I had them right away and didn't have to pay for shipping.
![Wink ;) ;)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
I'd recommend getting some of the tubing as well. Helps protect the word from dust and the elements. It only costs a few bones.