The loser runs the full stairs of a local stadium, arena, or parking garage top to bottom for a rep count the league sets. A leaguemate counts reps aloud through a megaphone. Simple, free, and legal everywhere with public stairs.
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.
Seen in the wild: fantasyleaguelottery.com