Take Note that my controls are different from most people, here is a image -

You will need a turbo controller of some kind or if you are a keyboard user make a macro.
You will also need a decent PC that can stay on for 10 hours or sometime around there.

Make the Versus CPU level 5 and put the timer on the fastest setting in the game settings.
Make your turbo controller or macro be Square and Cross (I use a Ps4 controller and a fight stick)
You need it to spam Square because that will cause your character to use their Smart Steer (The game's version of a auto combo) and the reason for it to spam Cross in for you to rematch your opponent. Make your opponent someone easy like Chaos and go to sleep or do something for 10 hours and comeback. When you come back remove your macro or you remove the heavy object from your turbo controller in order to manually go to the main menu. When you make it to the main menu it will give you a prompt of how much you have made.

Even if your character losses the one out of 100's of battles you will still get money so do not worry.

With all the money you made you can now get those achievements that are crazy to get.
I hope you enjoyed this guide and good luck!