Farming Lab nets people multiple mirrors in my guild early on (70-100 exalted per mirror). I farmed them differently for time runs which rewards the top speed with a jewel which on Cruel and Uber difficulties sells for 5-7ex per. The enchants which can sell for up to 8ex are a huge chunk if you have the ilvl 84 hubris helms to enchant early on or if you hit melee skills on Daresso's or Abyssus helms. Like other end game content, the more you do it the easier it gets. You pretty much will memorize all of the layouts and locations after a run or two a day.
Nothing though for money beats Shaper, Uber Atziri, and Chayula on week 1. Fyndel right now is the highest in our guild with 8+ mirrors farmed from Chayula and Shaper runs. They are very organized and sleep very little the first week though, its not something easily done.