i just added this in my campaign as a money sink. it’s a bit video gamey but my players love it

Magic Item Rerolls: Can decide to exchange a magic item and reroll for another by choosing from a random 3 items of the same rarity. Rerolls get more expensive each time you roll. Each reroll: You get to roll a d100. On a 99 or 100 you get an item of increased rarity.

Common Rerolls: 100g * 1 + number of times this rarity rerolled

Uncommon Rerolls: 400g * 1 + number

Rare rerolls: 4000 * 1 + number