To get a lot of money, REP and Speed cards quickly, complete short events. Since all events give almost identical rewards regardless of the difficulty, just keep repeatedly completing the shortest events. The fastest event in the game is the "Drifting The Block" drift trial. It becomes unlocked early in the game, when you do drift trials for the first time. It is the perfect farming spot for money, REP, and Speed cards. This event can be completed in 90 seconds, and since it is a circle, you finish at the start and can instantly replay it. Each time you finish the drift trial, you will get approximately 12,000 credits (17,000 credits if you sell the Speed card), 120,000 REP, and a Speed card. You can get approximately 3,600,000 REP and 510,000 credits per hour using this method. Keep replaying the "Hyperspace Circuit" race. It becomes unlocked during the final act, at the end of the game. It gives 31,000 credits (if you sell the Speed card), 144,000 REP, and a Speed card. The event only takes three minutes to complete, including loading times and transition screens (with a fully upgraded car). It also immediately puts you back at the start of the event. You can get approximately 2,880,000 REP and 619,980 credits per hour using this method.