The Negative Money Glitch or No Money Glitch was first discovered by TedGN. By getting your money balance into a negative value, you can purchase any car or upgrade for free, as long as the negative balance is kept up and the respective car has been unlocked.

You can set it up straight at the start of your run.

1. You start off with 5000 CR. First, I recommend you buy the Malice to lower your balance to as close to 0 as possible. (-4000 CR left, 1000 CR remaining)
2. Go to the upgrade shop, select the 'Engine' category, and look for the Modified Tuning Kit (price: 1000 CR).
3. Quickly tap left or right and then [ENTER] with a super short delay (like 0.1s). It worked if you selected the Turbo or Nitrous but not if you selected the Modified Tuning Kit.
4. Purchase the upgrade and you’ll see that your money balance is negative (-600 CR if you went for the Turbo, -700 CR if you chose Nitrous).

Now you can buy any car and upgrade for free. Remember to keep your balance negative, else you will need to set up the glitch once more.