It looks like today’s challenge will only pay out 3x the difference between your accumulated experience going in and 5000 which is the max available. So for me this meant I spent 150 gold to get 3x29 IIRC. I could pay 100 gold and play the adventure normally and get more than 29XP. Even at 3x it is only a little more than you’d get for a normal play through. Definitely not worth the extra 50 gold. Just avoid that last play through as it is a bad value for your gold.