One particularly hot commodity was Clash of Cultures: Civilizations, a 2014 expansion for Christian Marcussen's 2012 large-scale civ game Clash of Cultures. If you look at the sales history of this item on the BGG marketplace, you'll see that it regularly sells for at least US$100, with dozens of sales over US$200. Some folks swear that this expansion is essential for the game experience, yet copies are relatively hard to find.
A solution for this situation will arrive in November 2020 with the publication of Clash of Cultures: Monumental Edition by WizKids, with this new edition of the design including the original base game, the Civilizations expansion, and the Aztecs expansion, while featuring new cover art, new graphic design, and miniatures for the Seven Wonders. Here's a brief description of the game:
In Clash of Cultures, each player leads a civilization from a single settlement to a mighty empire. Players must explore their surroundings, build large cities, research advances and conquer those who stand in the way. The game features a modular board for players to explore, 48 distinct advances, seven mighty wonders, and loads of miniatures and cards. The winner will create a culture that will be remembered and admired for millennia.