Do drag racing until you beat it. By now you'll have some decent cars and the rest of the game should be pretty easy.
Brakes Bonus: Beat 7500 points in Pressure Tunning 2.
Unlock Chassis Bonus: Beat 5000 points in Pressure Tunning 1.
Unlock Controls Bonus: Beat 5000 points in Engine Tuning 3.
Unlock Drivetrain Bonus: Beat fifty points in Dyno Run one.
Unlock Engine Bonus: Beat 100 points in Nitrous Tuning 1.
Unlock Exhaust Bonus: Beat 2000 points in Engine Tuning 1.
Unlock Nitrous Bonus: Beat 175 points in Nitrous Tuning 3.
Unlock Suspension Bonus: Beat one-hundred points in Dyno Run 2.
Unlock Turbo Bonus: Beat 150 points in Nitrous Tuning 2.
Unlock Wheels Bonus: Beat 4000 points in Engine Tuning 2.