Coins

Coins are a vital part of succeeding in Jamestown. Gained via playing and/or winning levels, they are used to unlock a variety of items available in the Shoppe - such as new Ships to enable the player to approach challenges differently, or new gamemodes (i.e. Gauntlet or Judgement Difficulty).

Coins are gained when a player plays a level (any of them), and the amount awarded varies based on certain factors. Those factors are; the base, the completion, the difficulty, and the boss.

The base factor seems to rely entirely on what level is player - i.e. the First Level is awarded a base factor of 75.

The completion relies on the distance travelled through a level (or so it appears) - so one should be technically capable of killing no enemies (apart from the boss) and still achieving 100% as their completion.

The difficulty multiplier changes as the difficulty on the level is increased or decreased and ranges from 2x to 8x (or more).

Finally, the boss multiplier appears to be constant regardless of what boss and on what difficulty - sticking at 2x.

All of these multiply together to give the total money gained from any level. So therefore, it is in a player's best interests if they're attempting to earn money, to have the highest difficulty possible on the hardest level possible where they can still beat the entire level (or a vast majority of it).

Trivia:
The in-game money is Ducats. Ducats are gold coin, originally struck with the face of a duke. (Ducats comes from the italian word ducato). From around 1200 to the first world war, multiple ducats were issued from almost every european nations.