Car Mechanic Simulator 2021

The easiest way to get cash is to buy cars from the junkyard, wash/weld/detail them, and sell them as-is. See my guide here for how to buy a car from the junkyard:

At your garage, you'll need to purchase the car wash for 1750 CR and the welder for 5000 CR. Head to a toolbox inside your garage and press .
Press or to select the Garage and Tools tab.
In the Garage Expansions, select Carwash and hold to purchase it.
In the Tools, select Welder and hold to purchase it.
Go to the car you're selling and press to open the pie menu.
Select Move the Car in the bottom left and press .
Select Car Wash in the upper right and press .
The wash is behind where you spawn. Turn around and press to use the Car Wash, and again to confirm.
When the wash is complete, move the car to the lift in the garage using the steps above.
Ahead under the dart board, next to a tool box, is the blue welder. Press to use it, then select Move Equipment at the top and move it to the lift with the car.
To the left of where the welder was is the Interior Detailing Toolkit. Move it to the car the same way as the welder.
Press to use the welder. It will cost some CR. Press to confirm.
Once the welder is finished, go to the detail cart and press once to use, and again to confirm. the detail is free.
When complete, press on the car and select Car Status from the upper right with .
Press to got to Car Summary, and press to sell the car. You'll see your profit in green.
I've made anywhere from 800 CR to almost 10,000 CR per car this way, and it only takes a couple minutes at a time. You can buy as many cars as you have space for if you have the funds, so you can batch 4 or more at a time once you have the CR.