If you want to buy a duck for your farm, you will need to do two things. Firstly, you will need to save up enough money to build a Big Coop. That will cost the player 10,000g, and they will also need to gather 450 wood and 150 stone. Then once you have a Big Coop installed on your farm, you will need to head to Marnie's and purchase a duck; this will cost the player 1,200g per duck. However, as any Stardew Player will know. The biggest challenge will be picking a decent name for your duck.