well the breen absolute zero set sells for 100,000 a piece... three pieces are pretty easy to get, it's just the middle mission with the puzzles and flying around the sector that takes time... i'd average it out at around 90 mins work for the three pieces, 300,000 for them, add another 100,000 or so for all the various drops you'll find around while doing them, and you can pull an easy 400,000 to 500,000 for 90 mins work...
That's the quickest way i've found of making EC's aside from DOFF missions... i'm close to 10,000,000 now, probably aiming to hit 20,000,000 by the weekend if things go according to plan
M