FBA sellers must pay storage fees for products stored in amazon’s warehouses. The current prices for US-based warehouses vary by time of the year and product size (standard or oversize products):
In the last days, amazon added a possibility to set up automated repricing for your products using a flat file. The file allows to indicate the minimum and maximum price per product as well as the pricing rule. Amazon will then reduce your prices automatically to maximize the chances of winning the buy box.