You will get 30 million or so from all the other achievements combined. For the rest of it start a Skirmish on Burial Mounds against a Normal AI. Set the No Rush option to 20, Fog of War to None, Units to 500, and game mode to Supremacy. Tech up an Air Base and build three Tech 3 strategic bombers. When the No Rush timer expires (you can see how long you have left by pressing the back button) send your bombers to take out the enemy ACU and start making gun ships (if you are UEF, you can create Tech 3 heavy gunships, otherwise use the Tech 2 ones). Send the gunships to kill all remaining units (start with engineers, then any anti-air units) and turrets, then blow up all factories and mass extractors. Make sure you leave power plants alone (the Supremacy game type ends when you destroy all of their buildings, so you have to leave them some buildings and power plants are a good choice).
When the enemy is pacified, self-destruct all of your units except your ACU and Tech 3 engineers. The next step is to make a template that has a Tech 3 mass extractor adjacent to four Tech 1 mass storage devices (select one of your existing setups by dragging a box around it, and then press right on the D-pad, use the LS to pick a spot from 1-8, and then hold down the A button for about three seconds until the animation is done). Get two groups of 3-5 Tech 3 engineers and have one group place the template on all the mass points on each side of the water, and don't forget the middle island. While that is going on (it can take an hour or two to get them all planted) you can build four Tech 3 power plants and then reclaim all the other buildings in your base except for the mass extractors and their mass storage. Then upgrade your ACU with the improved Resource Allocation Upgrade, and go to bed. In 8 hours you should get around 70-75 million mass, so you may need to leave it on two nights if you haven't done the campaign yet. You can check along the way by saving the skirmish mission and when it says "Saving profile" it is checking for any achievements you may have earned.
You may want to get Firestorm when doing this one as well.