What is the best location/method in the game to obtain money quickly for purchasing all the collectibles?

i farm money in midnight bay inside the secret monkey room in the ship

The fastest method to obtain coins in the game is by entering the secret room in Midnight Bayside, breaking all the creates containing coins & morph pallets, exiting the room, & re-entering. All the crates will have respawned along with the coins & & morph pallets inside them. This is a method that's used for coin grinding in a 100% speedrun.