If you are a Play Music subscriber you are in luck!
Google is currently running a promotion offering an extra 10% off the current Google Play store price for movies and TV shows, music albums and tracks and paid apps and games purchases in the store.
Best of all, it works even if you are running a trial Play Music subscription!
This promotional discount does not apply to books, newsstand, in-app purchases, or device purchases and it cannot be combined with any other offers. There are currently no details about when this promotion runs out.
Details on this promotion can be found on this Google Play page.
If you are on the look out for Christmas stocking fillers, Google is running also a promotional offer on the Chromecast V2 - buy any 2 for £50 and they throw in £20 Google Play credit with each Chromecast, making that £20 credit stretch a little further with the 10% discount.