Money or Pokédollars in the Pokémon franchise has never been genuinely essential, as you always got plenty to spend from the amount of Pokémon battles throughout the game. Yet in Pokémon Legends: Arceus, money is essential for purchasing upgrades or evolution items, like the Linking Cord.
The best way to farm money quickly is to fight Alpha Pokémon repeatedly to get the valuable items they drop—Seed of Mastery, Grit items, and EXP Candy. These items sell for quite a bit, and doing this over and over again is a money farm. But only sell what you don't need, or the items you already have a lot of.
Alpha Pokémon always stay in the same location. This means upon defeating them, you can fast travel back to Jubilife Village, return to the Alpha, and they will have respawned to battle again. Rinse and repeat.
You can find Alpha Pokémon all over the map, so take note of any close to a fast travel point and ones that are a lower level, as you need the item drops, not the EXP.
Remember, these new Alpha Pokémon are no joke to fight. They are the maximum size value of that Pokémon and have glowing red eyes to boot. These are higher levels than anything else in the area, so get ready for a hard fight, especially if you're early on in the game.
For more help with Pokémon Legends: Arceus, we at Pro Game Guides have you covered.