CD Projekt Red is collaborating with Bungie on this crossover.
Art showing cosmetic items for Destiny 2 with armor inspired by The Witcher series from CD Projekt Red.

November 28th marks the start of Season of the Wish for Destiny 2. With the arrival of that new season comes new seasonal cosmetics. The Season of the Wish will allow Guardians to dress up in a variety of cosmetics inspired by Geralt of Rivia and The Witcher franchise. The crossover content includes armor ornaments, a Ghost shell, a ship, Sparrow, emote, and finisher.

Typically, these special seasonal cosmetics are only sold for the in-game Silver currency, which can only be purchased with real world money. The exact cost for these cosmetics has not yet been announced. If it follows the pricing that the previous Assassin's Creed crossover armor went for, players can expect to fork over 2,000 Silver for a full class armor set. That comes out to about $20 (USD) per armor set.

Bungie, what's left of them, will also have a sale through the aptly named Bungie Store. The sale kicks off on November 24 and will see the return of "limited quantities of previously retired Bungie Rewards."

Promo art for the Bungie Store promoting a big sale and some free emblems with each purchase.

Those participating in the sale will receive Darkstar, a free emblem with all purchases, during this period. During the sale, all orders in the 48 contiguous US, EU, and UK will have a $7 flat rate shipping. The Bungie Store sale ends on December 1 at 8:59 PM PT. Additionally, the new Wishing Well emblem will be available for purchases made on November 24 or later during the Season of the Wish.
Season of the Wish is the final season before Destiny 2: The Final Shape expansion is released. It's also the last traditional season of Destiny 2 ever as Bungie is switching over to three "Episodes" per year.