I can usually pick up 800k+ just doing all the Korriban/Dromund Kaas/Balmorra/Nar Shadda heroics, in less than 4 hours (it helps that Balmorra and Nar Shadda have two of the most mob-pack-filled Heroics (Resistance Sympathizers and Terminal Injuries, respectively) out there). You don't make money on Heroics from the quest rewards, you make it from the mob packs you kill along the way and the loot you sell off that the mob packs dropped. Alderaan also has a quite lucrative Heroic, Sabotage, that features quite a number of mob packs that you can loot for creds.