If I had to come up with 5m as quickly as possible, I would do a bunch of Treasure Maps, a socket scroll (although rare) is worth 4.5m, and I have gotten them in the past with regularity on Cleverly Maps or better.
I am no stranger to being tight on gold, when I began the shard, I set up a rune book that had high gold drop mobs. Examples here would be Rune Beetles, Hiyru, Oni, Skeletal Dragons, Dragons, Deamons, Balron and Titans. All of these examples drop either high gold (1-2.5k), or have the chance of dropping Treasure Maps, and can be recalled to and from freely (not in a dungeon). With enough entries in a rune book like this, I was able to go from start to finish, and in some cases, the time taken was enough to let them respawn.
Respawn times are an issue that have been brought up here on the forums recently, and Staff have acknowledged it being a problem, given the size of the shard now. So hopefully we will see the spawn rates pick up in the near future.
Try hunting areas with high drop chance of augments, remember a Parry Augment can sell for 4.5m, and some of the other augments are nothing to sneeze at. I suggest to NEW to try inside the Fairy Gate at Ilsh Mushroom cave, and even the Travesty Citadel.
For me, I hunt nearly exclusively in Fel, as the tyrant spawn rate seems to be higher than the paragon spawn rate of Ilsh, not to mention, it is VERY rare to receive a paragon chest, while I get quite a few tyrant chests. These chests all contain one treasure map, regs, gems, gold and one "rare" item.
I hope this helps, and good luck out there!