I know there has been a deal for Xbox Games Pass already, but it didn't mention this (which I think is the best part).
When you sign up for a trial of (or pay for) Xbox games pass, you get 20% off all games in the pass. Therefore, if you wish to purchase a game that is included in the pass, you can sign up for the trial, and purchase the game for 20% off the listed xbox store price, then cancel the trial before you are charged.
Here are some examples of titles that can be purchased at a discount:
Mad Max USD$14.99 (USD$4 off) on US store
Blood Bowl 2 AU$43.96 (AU$10.99 off)
Brothers - A Tale of Two Sons AU$31.96 (AU$7.99 off)
DmC Devil May Cry: Definitive Edition AU$31.96 (AU$7.99 off)
A lot of the titles can be found cheaper elsewhere as physical copies, but there are a couple of good deals to be had. This is also good for gamers who prefer digital.
As a note, much better deals can be found using this method on the US or other region stores (as per the Mad Max deal above).
This deal can be combined with xbox store sales to maximize discount.
Blood Bowl 2 AU$43.96 (AU$10.99 off)
https://www.mightyape.com.au/games?q=Blood+Bowl+2&source=lan… $24
Brothers - A Tale of Two Sons AU$31.96 (AU$7.99 off)
https://ebgames.com.au/xbox-one-211065-Brothers---A-Tale-of-… $15
DmC Devil May Cry: Definitive Edition $19
20% Off RRP off old games isn't good.