If the league can pull strings with a local baseball team, the loser serves as bat boy for part of a game, in full uniform, at an age where that is deeply embarrassing. A minor-league or rec-league version works when MLB connections are scarce. The stadium PA mentioning why is the cherry on top.
Budget note: this one costs nothing but dignity, which makes it a strong pick for leagues that would rather spend the pot on the champion than on the loser's downfall.