Find one of the bird shooting challenges. They are usually easy to find; just listen for shots and watch for a lot of birds circling in the sky. Accept the challenge and intentionally lose. The wager will then double. Repeat this until you have just enough money to make one more bet. Then, watch the sky and wait until you can see the amount of birds you need to win the bet. Accept the challenge, then go into Dead Eye mode. Take down the proper amount to win. Note: It may help to have moonshine or chewing tobacco in case you run out of Dead Eye. After you win the bet, put on your bandanna and kill the man you bet against. Loot his body and he will have the same amount of cash as the final wager. The more money you have to work with, the more you can make. It is possible to loot over $20,000 from him.