How to Allocate Budget for RMN in Pet Treats on Target, Chewy, and Amazon

We are entering the realm of Retail Media Networks (RMN) for the first time with our pet treats brand and need guidance on budgeting effectively. Specifically, we'll be advertising on platforms such as Target, Chewy, and Amazon. Are there best practices for setting aside a percentage of either cost of goods sold (COGS) or gross sales for these efforts? What percentage range should we consider when planning our budget for RMN, especially if our goal is growth rather than just maintaining our current position?