Army of TWO The Devils Cartel

I think I have found out the best way to grind money, if you don´t have the Outside Contact - Overkillers like me.
Go to Outside contact -> Level 16 "Suicde Run". Difficulty Insane for max Difficulty Money Bonus.

Trivia: All you have to do in this short section is to drive a Car to a Destination. It isn´t possible to die in this level.
- Choose to drive - the AI shoots. You should do this because the AI will do higher combos on the MG.
- Drive as fast as possible. Avoid obstacles like the MMG cars and push the whole time the RT (driving) button down.
- If you have finished the level don´t use "skip" (the back button) in the menu/level stats. Choose-> "next" (A button) until you are on page 4 -> then quit (to main menu). Because otherwise the game will force you to do level 17. So you have 2 loading screens instead one loading screen. To do Level 16 again you will have to go to the main menu anyway.

What you have to keep in mind:
You will get the most money in this section if you score high combos. So overdrive as many enemies as possible. The best Combo possibility is on the end section of this level. -> In the last turn before you drive downhill it is possible to overdrive 5-6 enemies, if you hit all of them and on the downhill section another 6-8 you should get a very high bonus. Aim for the gate directly before the MMG in the end because sometimes 2 enemies run 1 secound before the cutscene starts onwards you -> 2 more kills for your last combo.
Another nice section for combos is before the big plaza. There are many enemies but most important: If you stay on the right side directly before the plaza you can hit 4 Enemies at once.
Here are my datas: In my first trys I was poor and could only achieve 3200$ with a time of 2:02. After a few tries and knowing the "course" I knew where I could do combos. So I have managed it to get constant 4200-5200$ in 1:32-1:40 minutes. Because of the shortness and high reward, this Level has the highest effiency in the whole game for farming gold.

I know this sounds (and is) boring. But even if you do this for only one hour you should earn around 100.000$ (loading times eat some time too)
Too compare: I have played the whole game through on Normal and Insane and had only earned for 2 complete playthroughs around 500.000-550.000$..

I am posting to help with the money grind which is needed to buy everything including the 30 weapons. I beat the game twice and still needed around $200,00 to buy everything. I did buy quite a few upgrades I didn't need, but there will still be a grind in the end. This method works best with 2 human players. You can get about $12-15,000 in one run and it only takes a few minutes.

Load up the mission "Last Resort" and checkpoint "17. Holiday Retreat."

Play normally until you breach the big room. Once, in there, you should have a full overkill meter. You and your partner need to go into Double Overkill (this seems to help with the earnings quite a bit).

The first enemies spawn in this order.
-Top right hallway. 2 enemies.
-Bottom right Hallway. 4 enemies
-Front right bottom Hallway (under the AI squad up top). 3 enemies.
- Top right hallway. 2 enemies.

Continue through the level and try to fill your overkill meter before you are told to go to the elevator. If done right, you can go into Double Overkill again in the last hallway.

When you finish the chapter, quit to the menu, set up another game, and load the chapter back up. This is the fastest way to make money that I have found. Any feedback is welcome!

If you have the Overkill Edition of the game load up the contract under the Outside Contact mission and when you get to the brute just kill him and no one else. After the brute is dead run down the hill and position yourself to the left of the plane that is in front of the truck for the end of the mission. Turn around and you will see another plane in front of you where enemies like to run into and hide. You will see a giant yellow crane over top of this plane if you are in the right place. Now if you look just to the right of the plane you will see enemies spawn in right there. Just keep killing these few enemies as they spawn in and ignore all the enemies out in front of the plane. These enemies will spawn infinitely until the horrible AI finally kills most of the other enemies in the area which takes forever. Every time I did this I made between 120k and 135k with a 10-15 minute completion time.