This is easily done through the use of the in-game admin panel, which can be opened by pressing
+
simultaneously, so long as you are the host of the game or have been promoted to admin of the game you are in.
Bring up the admin panel and from there use the drop down menu at the top of the panel to select "economy". You will then see an option there to change the balance of player and you can then simply give yourself 1,000,000 credits (or however much you desire) to pop the achievement. Enjoy! :)