Google is currently holding a sweet deal for anyone who buys a Chromecast or Chromecast audio from the Google Store: if you buy one of them (or better yet, both), the company will credit your Google account with $10 to spend on Google Play apps, games, movies, music, etc.
However this deal’s good at the Google Store, the California company hasn’t specified whether this promo’s good at other retailers or not, but based on previous specials, you’re probably better off just buying it right from Google.
You need to make your Chromecast purchase from February 3 to February 24, 2016 in order to qualify. The credit will be added to your account by the end of May, and you’ll have until December to redeem it.