This can grinded relatively quickly on Sandbox Mode.
Set starting money to unlimited and starting era to Modern Times. The other settings don't really matter too much.
As soon as your game starts pause and buy the 'Building Permit' Edict. What this does is add 10% of the cost of any building to your Swiss Account, but only when the building is complete.
Next you need to lay a long strip of road and unpause the game, now start placing and quick building expensive buildings, I found Cathedrals to be ideal, each on adds around $3000 to your Swiss Account. If you build the Nuclear power station you can then place Stadiums, which add $4000 each time (though they do take up more space) .
I got this after I already completed the campaign, but even starting from $0 in your Swiss Account you would only need to build around 65 Cathedrals or 50 Stadiums.
Hope this helps.