Just as an update for those looking to extend expiration for cheap. Looking through the Rewards site, it appears that the game "Tiny Troopers" is now gone that used to be cheap. However, I just looked through the entire Games Special Offers and here are the current lowest:

Wickland - 50 points (normally 300, "discounted 80%")
The End: Inari's Quest - 100 points (normally 1150, "discounted 90%")
The Dweller - 150 points (normally 1450, "discounted 90%")

I did Wickland for 50 points and it was immediately in my account, extending my expiration. 👍