Typically $35 a piece right now you can grab two Chromecast Audio dongles for $15 off. For a total of $55 you can add streaming music to your favorite speakers. This is a limited time offer and is currently available at Best Buy, B&H Photo, Google Store, and Target. All stores offer free shipping sweetening the deal, and I assume in store pick up is available as well.
Chromecast Audio allows you to stream your favorite songs or internet radio stations to speakers you already own. It even offers multi-room streaming.
Source: Droid Life