Rework How to Get the RoD
As you know, the Wizard sells the Rod of Discord for 10 platinum (excluding happiness discounts) when he's in the Hallow. This method, however, is incredibly uninteresting and cheapens the item to "just another thing to buy." The 10 platinum is an insufficient blockade that could be overcome with only a few defeats of a given boss. I personally have found myself having dozens of platinum coins well before defeating the WoF. As such, I've devised a few solutions to obtaining this item rather than "pay money and get it lmao."
1) Make a Shrine for the RoD
This would be the most ambitious method, but I'd argue that it is quite worthwhile. Not only would having a RoD in some kind of shrine emphasize its importance, but it would also allow for worldbuilding and the execution of lore. The question of Pre-HM obtainment could be countered by making the RoD similar to Murasama, in the sense that it would unlock its power upon the defeat of a boss (WoF in this case).
2) Give RoD a tier-locked Dungeon Chest
Similar to Astrum Aureus and his Astral Chest, the RoD could be locked in a chest in the Dungeon that could unlock upon the WoF's defeat. This could work to make the RoD feel more deserved. You could also lock it behind Queen Slime to make her more included in the game progression, as it's pretty common for people to skip her.
2.5) Give Queen Slime a RoD Drop
As an alternative to Idea 2, you could have Queen Slime drop the RoD directly. This would be effective enough, though might overcrowd her drops.
3) Simply Buff the RoD Drop Chances