Sure the iPod is portable, but not when you add the Wadia dock, amp & speakers and so on.Why does it no longer become portable? You just pull it off the iTransport, plug in your headphones and away you go!
I admit I am not knowledgeable off all the other ways, but this is a very easy way to have a music server based system, one you can take with you to boot.
As for money, I don't know what that setup you suggest costs, but the iTransport and an iPod seems reasonable to me.