Dirt Rally

There is quite quick method of making money with absolutely no effort and skill. I'd strongly recommend it at the beginning, before you can afford to buy more expensive rally cars or even rallycross and hillclimb cars. Consider this as a stable method of earning money at the very beginning of your career.

Before starting, turn off all assists! You want to max your income from single event and extra 18% will help with it. Don't worry, you won't be driving but I strongly recommend getting used to those settings, as the game may only be fully experienced by driving without those assists. Start custom championships with 6 events, 12 stages and maximum difficulty unlocked. Car and class don't matter, pick the car you have (probably something from 1960 if you are at the beginning). Start your first stage, hold your handbrake button and after a stage has started, immediately retire. Obviously, you would lose your event but you would get around 10 000 for your 16th place. Start next event and do the same steps as in previous race. This championship shouldn't take more than 10 minutes and you will earn around 60 000. It's not that much compared to hillclimb or later stages in rallycross but Rome wasn't built in a day. You would have to earn quite a bit of money for your cars in different classes and it is definitely faster than trying to make perfect times in championships in your vehicle from 60s which will net you 30 000 after finally winning it.

The quickest way to earn money in Custom Championships is to do Hillclimbs on the hardest difficulty you have unlocked. Each event win on Masters difficulty will net you ~100,000+ credits (with as little damage and as few restarts as possible) in 3-4 minutes (plus load times). Set up your own championship with four events and one stage per event. That's ~400,000 credits in about 30 minutes. Lower difficulties will earn you progressively less. Repeat as necessary to unlock achievement.

You can skip your first run by pausing after the start line and selecting 'Abandon Run,' and then just focus on the second run with the final time to beat as your delta.

Now sometimes the game will throw the full course into the mix, which will take 9-10 minutes per run. Usually it'll just be the individual stages. There's no way to choose which you'll get. It's entirely random.