Requires 63e120.
The blueprint that brought me to the magical number was Riflescope. Which took a long time to get, as it only appears in the Forest Pack with a relevant number (7,41% propability to drop in this pack). I got 8 blueprints and leveled it to 91. Made a base income of 11e105 and with boosters a merchant revenue of 142e117.
But it all depends on your meta-multipliers that you get for the ingame achievements and most of all the artifacts. With lower meta-multipliers you might have to push for weather station or even further.
As a reference these were my multipliers, when I reached 60e120 (needed for the merchant achievement).
Income: x1.4e33 (very relevant)
Click: 35,741% (very relevant)
Offline production: 134,600% (not much relevant)
Ore output: 24,158% (not much relevant)
Research: x46e6 (semi relevant)
Merchant revenue: x2,7e9 (very relevant)
Main workshop level 60 (no income multipliers after this level)