http://www.techradar.com/news/pokemon-sun-and-moon-review

Update: One year after the release of Pokemon Sun and Moon, the sequel titles are coming to the Nintendo 3DS this week. Called Ultra Sun and Ultra Moon, these games will extend the story of these original titles and introduce a host of new features. They're also Pokemon's last outing on the Nintendo 3DS platform before the franchise moves over to the new Switch console. 

With these new releases landing, you might find that the original Sun and Moon titles appear in the Black Friday sales this year. Pokemon games tend to hold their value very well, but these sales are your best chance of picking the games up at a slight discount.