There is a glitch in the Winching Challenge that can be exploited to gain a considerable sum of money very fast.

I know this topic is two years old, but go fight large amounts of either Chinese troops or the Allied troops. 50k per enemy kill, plus a payout from enemy vehicles destroyed, you'll be rich in no time. If you're friendly with both, then keep going and stop reinforcement calls from getting through. When necessary, save and reload the game and when you come back, you'll still be Friendly.