So basically implement a gold sink that allows players to create gold faster in the game. Dungeons are the reason why we need gold sinks. It sounds nice, but logically.. you're legitimately directly feeding the problem with its own solution. <_>
If you say thats the problem then I'd imagine dungeon runners would make that much worse since they gather a group of players run the dungeon for them then depending on the player they demand 50%-90% of the reward.
My take on a fix for this would be:
1. Make it so no one outside the dungeon's range can enter.
2. Make it so its actually possible to complete the dungeon without being required to be 20+ levels higher than it's limit (right now it'd take a full group of players with orange-yellow +15 items to beat a dungeon within it's limit)