Google again comes with the an offer for the Chromecast buyers i.e. Google is giving free trail for 90 days of all services on chromecast if you buy this device before 30th September 2014 in UK, France, Germany, and Canada, but not in the US.
The promotion is valid for those that purchase and setup a Chromecast on or before September 30th and is only available for new Google Play Music accounts. You can redeem the offer after setting up your Chromecast and visiting chromecast.com/offers. Full terms of the promotion are here.