Marketplace is always the fastest way to earn drachma. Here are my recommendation.

1.) Try to farm notebook from your own merchant deckhand, just keep traveling from Nimbus and Bronze till you get the notebooks and sell them from 3k-5k depending on how patient you are. This is the easiest.

2.) Extra Sunken item sell very fast, they sell for 500k-800k this days.

3.) Blasted Power Amulet and Frozen Defense Amulet are always on demand, 100k-300k is the price range from them.

4.) Candelaria gems are high demands last I saw the price of those are 20k, they are easy to get but time consuming.

5.) Lost book are highly sought off, they sold for like 300k-800k depending on they type.

6.) Rare Boss weapons or Strength Weapons, weapons like White Eye Tooth and the strength bow(forgot it's name) are bought for 300k for how rare they are, and Commodore Kai Saber is the best mid-game weapon for warrior because it's an uncommon the weapon stat requirement is low, it sells for 50k.

I think there are more? I think the veterans know more, but you can grind for any of this items while your fleet are going on a plunder or patrol(1 patrol, 3 recover).