Win the last career race wich is the final boss to unlock the car "Penetrator 8086" the fastest car in the game, then select the "Race36 - Night City" since the prize for winning is 100k it will be easy, just repeat 10 times and you will have the achievement accomplished in no time.
I know it seems like a simple tip that many of you must have realized naturally but I leave it here anyways, cheers.