-Hang around in the debris fields and use turret mode, etc. to shoot the floating canisters. Haul in the scrap metal and sell it at Baltimore Shipyards, if you can. You will get about 20 credits per piece of scrap metal, and you can get easy money this way, if you don't care about waiting.
-For easy money, you have a good relationship with the Rogues, Hackers, and Outcasts. Go to Mactan Base in the Magellan system. Save the game. Exchange your ship for a Dromedary. Purchase as much Cardamine as you can. Leave Mactan and go through the old jumpgate from Magellan to New York. Staying in the Badlands, fly from the jump gate to Buffalo Base. One there, sell all of the Cardamine. Leave, go back to Mactan, and repeat. By the time you can purchase a entire cargo bay full you will be making more than 100,000 credits each time.