https://wccftech.com/todays-list-of-apps-and-games-that-are-on-sale-at-the-play-store-including-the-swords-of-ditto-and-more/

Most of the apps should be on sale for the next three to four days. If you see a reduced price next to the original, then it's on sale. Otherwise, it is full price. Once you purchase an app, you can install it on any Android device with the same Google Play ID.

Today’s List of Apps and Games That Are on Sale at the Play Store Including Neverwinter Nights: Enhanced Edition and More