Although PhyrexianZ's methods will work, I believe I have found a solution that is not dependent on greed spawn nor waiting for nighttime for them to attack.
TL;DR --> clear an island so no more greed spawns and sit in front of the dock greed portal monster and let it knock your crown off. Rinse & repeat 299 more times.
Per darkling1542 in the comments:
You should also do this with 2 controllers as this will give you progress for 2 crowns every time.
I cannot confirm this method of boosting 2 crowns but worth a try!
First, we will need to have cleared an island (destroying the greed mountain core with the bomb) so that no more greed will spawn on that island. This can be accomplished on any island but you will need to have at least reached the 4th island. A quick review of how to clear an island:
-reach the 4th island by continuously repairing the boat on islands 1, 2 then 3
-purchase the steel/iron/refinery
-upgrade camp to the max where you'll get an option to purchase the bomb
-escort the bomb to the mountain cave past all the portals (opposite of the dock side)
-pay 5 coins to enter cave and escort bomb to the core
-pay another 5 coins and escape the cave --> done
Secondly, you must not have cleared the monster on the dock. Again, this can be done on any island so if you've already destroyed that monster on one island, check any of the other 4 islands.
Lastly, once an island is cleared and you can now reach the dock without running into further greed, you can start the farming process by moving in front of the monster (without any coins on your person) and let it knock off your crown. Keep retrieving your crown and run back to the monster. Voila!