This event can be completed in 90 seconds, and since it is a circle, you finish at the start and can instantly replay it. It is the perfect farming spot for money, REP, and Speed cards. It becomes unlocked early in the game, when you do drift trials for the first time.
The fastest event in the game is the 'Drifting The Block' drift trial. Since all events give almost identical rewards regardless of the difficulty, just keep repeatedly completing the shortest events. To get a lot of money, REP, and Speed cards quickly, complete short events.