If it were an iTunes-only source, then an Airport Express at $100 new or $50 used would be an even more cost effective way to go (providing you have a WiFi router). But to be able to stream from other programs or web browsers would require Airfoil, a $25 extra piece of software and a few extra mouse clicks.
One advantage of the Airport Express is that you could stream audio to a remote location while having a different audio stream running on the computer and local amp if you wanted.
But for your application, the Audioengine W3 sounds like a good choice.
Steve