Will many people check the Promoted feed? I think there should be a feed that combines top posts by boost, activity and earnings. Could be a tricky algorithm to get right.
It is possible to get a top promoted post on some tags with a few cents, but that depends on people actually looking there. I've had people boost my posts for me with a dollar, but they still didn't make much. It's still down to getting seen by a whale and they may not be checking promoted.