DISCONTINUED
Probably still works...

Development restarted by EPICBOSS84. More features planned.

Features:
Buy items selected during part installation with the button B. Buy tuned version with button N.
Discounts taken into consideration.

Installation Instructions:

Unity Mod Manager Installation
1. goto Unity Mod Manager and go to files and click on "Manual Download" button on the first file. Place the files anywhere(Not the CMS2018 folder)
2. Now run the .exe file, if you get any warnings when you open it click on "More Information" and "Allow" (There is nothing malicious within the program)
3. Choose "Car Mechanic Simulator 2018" in the drop down menu. If it want you to select the game folder do so(usually in "C:\Program Files (x86)\Steam\steamapps\common\Car Mechanic Simulator 2018") and then press install.
4. You are now ready to download my or someone else mod, that requires "Unity Mod Manager"

Mod Installation
1. Click on the "Manual Download" button in the "files" section and download it.
2. open the .zip file with WinRar, 7Zip, Windows 10 built in zip tool or another program that opens .zip files.
3. Extract the folder named "QuickShop" to your Car Mechanic Simulator 2018 Mods folder (usually in "C:\Program Files (x86)\Steam\steamapps\common\Car Mechanic Simulator 2018\Mods") or go to the mods tab in Unity mod manager and drag and drop the .zip and it should install it for you.
4. You can now enjoy the mod. Or not

Credits:
Puzzola75

Other:
Source