Tour the Galaxy; selling loot from Foundry missions; Starbase 24; Mk XII purple consoles from Children's Toys... When you have the capital, taking advantage of the fluctuating market during key sales or lockbox events is a good idea too.
Do the Dilithium mining every day. Get good enough to get rare particle traces. If you get the good ones and have more than one character active, you can get a couple of hundred thousand for little effort on the exchange.
Grind dilithium. Buy Zen. Buy keys amd fleet support packs. Sell on the exchange.
Do a grinder mission in the foundry. They shoot back now but you should be able to get some good drops to sell.
_________________ Nebula coffee is the best coffee
It is better than the replicator, but it's 50%. The same as almost every non-civilian vendor in the game - the ground equpiment vendor on ESD is pretty convenient, as are several equipment vendors near the beam in point on DS9.
The foundry grinders are pretty decent. In Battleship Royal Rumble I can typically earn 400-500k ec out of it. I would highly recommend DOFFing aggressively if you can. If you get good at it you can dump some of the better DOFFs on the exchange that aren't bound, but keeping a steady stream of missions running helps with the cash flow. I would specifically recommend looking at engineering missions -- there are research upgrade missions for all the space and ground items that are 8 hours long. If you have halfway decent DOFFs you usually get a blue quality --- which is good vendor trash.
I think the special items tag might be only 40%. But if you go to ship equipment, then the hanger tab and then sell, that I know is 50%, unless they changed something. Always do a quick check of the price of the item and make sure youa re getting 50%.