Mission accomplished, played for one month without paying 1 €.
During this period, 30 days, I earned a little over 100k gold, enough for 2 months.
I found the easy way !
1) Level alts to 100, letting them build Inns for free weekly Treasure Hunter trait followers. This way, every gold mission gets 2x, 3x, as much gold. Garrison lvl 3 is not needed, lvl 2 is enough, for both the garrison and the Inn. Do missions for each alt. No need to gear followers above 600gear. But get them all to 100, if possible. How many ? A few. A dozen or so. All of them are obtainable by leveling.
I show half a dozen that I specifically get as they are way easy. The rest comes with questing.
2) Craft items, specially weapons (2H, staffs), Hexweave bags and most important, Steelforged Essences/Weapon Crystals (also Burnished Essence/Hexweave Essence, but less important as they target armor upgrades). These items upgrade weapons from 630-->645, 645-->660, etc. The cheapest upgrade sells for around 10K, the next in line for 11-15K.
There you have, a Gold factory getting you about 3K/day in less than 30 mins a day, with a single Mine, Herb Garden and Barn (for Savage Bloods).
I'll go for AFK now for a few weeks, holidays and all...
For the last day, I rushed a few achievements to get me above 21000 points on Netcownt.