So the basic of this method of farming is that whenever you leave an area through one of these dotted lines every enemy will respawn so that's what will be exploited here. Now the question becomes where to go, for me the area left to the hub worked best.

There you will encounter 2/3 enemies (if you are playing on hard 3 on easy 2) that you can just kill.
Leaving and going back to the area will respawn them.

Now for the optimal clear time and money gain you will need 5 different gadgets as well as one specific upgrade from Rungs.

1. The COG-SPLITTER (gives more money)

2. The RECOVERY POUCH (-!optional!- gives back some hp on your chronobreak, neat to have when u mess up)

3. The BLAST COUPLING (more DMG on your ranged attack)

4. The CHRONO-CONVERTER (more DMG when you have no rewinds)

5. The FORCE DAMPENER (more dmg in your slow field)

And you will need the TIMEWINDER CHARGE from Rungs.

The last thing left is to waste your rewinds to activate your chrono-converter.
Now that you have all of that, your basic combo on easy difficulties will be:

Slow field into charged ranged and then beat them till they die, the ideal way is shown in the video below. On higher difficulties you will have to deal with one of the flying enemies, but the strategies stay the same, just kill the ground guys first and then deal with the flying one.
https://youtu.be/Rc5W-yVtVpA