This is one of those trophies that are cumulative and are mostly farming. Doing main missions, stranger missions, gang hideouts, jobs, looting corpses, robbery, completing challenges, etc, count towards those 10,000 dollars. If you spent or lost money doesn't matter.
Two easy methods of farming are hunting bears in Tall Trees and selling what you get (meat, fur, claws) in Escalera, and winning Liar's Dice in the mission "Light, cameras, action", since you can get $200 dollars for winning instead of the usual $60.