Yep, it's 80K net income, i.e., after expenditures. And yes it does seem a bit daunting.

I don't think it's as hard as it sounds, though. By the time you meet the 90-settlement requirement, your empire will be amply sufficient to net 80K.

The key will be expanding in such a way that you occupy (at least with MAs or clients) the required provinces, and have one source of all the required resources (which have to be in your own territory; MA or client controlled resources don't count). Initially this may sound easy, but lead and silk are pretty scarce and way out on the fringes (at least from Rome's perspective).

It can also be maddeningly difficult to get the last couple of trade partners you need. Small factions get bumped off...or access to their capital cut...all the time. Seems like every time I gain a trade partner, I lose one somewhere else because they get conquered or lose their port.

All in all, the strategic locations & resources plus need for 20 trade agreements, make this really of a "economic/diplomatic" victory, rather than just purely economic.

In any case, once you've got the settlement, territory, trade partner, and resource requirements completed, meeting the 80K requirement can be done in a bit of a gimmicky way. Disestablish some of your armies, and cut the remainder to about half-size...you need to keep a mere 70 units, which is only 3.5 full stacks. This will massively reduce your upkeep, and free up at least 10K, maybe as much as 15K. Then just zoom your taxes up to Very High. Your public order will go bananas, but doesn't really matter, it's just one turn, and bingo, you win.