How hard (How much time in a day/week) is it to farm enough gold for this? Does anyone pay for sub anymore?

no, i can ah and pay for 5 subs in my offtime.

i can get easy 100k gold / 3 hours just half-afking AH so i wont pay never more

garrison from one character alone gives me about 30k a month

how?^^

have a tavern and an inn at level 3 as many high ilvl followers and a few with the treasure hunter trait , 30k per month is a bit low I have 5 maxed garrisons and I make 8-10k per day

Farm gold missions

On top of that you can have one of each or multiple of one profession and literally earn gold on a xx day cooldown... cooldown gold is easy gold that isn't really excusable. When crystals were around 500 a pop I could make like 10 a day and it took about 10 minutes of my time to make 5k a day.

I play maybe 10 minutes a day tops on most days. Managing one fully developed garrison and 2 other bare bones garrison, I make about 50k per month. I just have a lot of treasure hunting followers and log them in to send them on gold missions 2-3 times a day when I can. Then I use garrison resources from stash and trading post to buy draenic dusts and sell stacks of those. Trade in primals from daily traders and missions for savage bloods and sell those. Run enchanting hut and sell the temporal crystals. Sell stuff from salvage yard... I just vendor most and occasionally get a lvl 100 epic which I sell on AH.

At a bare minimum, get a fleet of treasure hunters leveled up and unlock the treasure hunting missions.

what is the tavern? i dont see that option in my garrison to build one of thous