Assuming heroes actually try to go after the treasure,
2 heroes: 75-125 [TH:150]
3 heroes: 150-200 [TH: 225]
4 heroes: 175-250 [TH: 250]
[TH:X] denotes when a Treasure Hunter is present (almost maximum income possible, along with a free shop item card because of the treasure chest)
So 225 G for 4 Heroes shouldn't be a pretty big failure for the Overlord?