When you wear Karamja Gloves (Diary Reward) in OSRS they lower the tokkul cost of all items in Mor Ul Rek and increase the sale price of all items to the shop significantly.
  • e.g. Onyx Price goes from 300k -> 260k.

Since the gloves aren't in-game, I suggest applying the boost to the Fire Cape or any other TzHaar related item.