Marketplace
Similar to this deal, but valid until 31 January 2017.
Screenshot from the Google Home app.
I was able to redeem it for both my old and new chromecasts.
Valid for 75% discount against the store price at the time the purchase is made of a movie or TV show rental from eligible titles on Google Play. Open to participants who have purchased and activated an eligible Chromecast device by December 31, 2016, and receive a promotional URL from participating Chromecast offer channels. Offer ends 31 December 2016. Discount applied at checkout. Redeem by 31 January 2017.
meh on the rental.
Although I did find the Die Hard movies on HD for half price.. so I bought that :)
Also I noticed I have an offer for 50% off a TV series. Others may have it as well.