Not to sound silly, but are you sure you haven't already unlocked Midas (Savage)?

If you haven't already done so, you could check your completed quests, under Sidequests -> Side Story Quests -> scroll down to Wandering Minstrel Quests.
Or you could talk to the goblin NPC next to the Midas entrance and see if there's an option for Midas (Savage), since this is how current savage mode is entered, not through the Duty Finder window.