There is no single advertising budget that is automatically correct for every business. The available budget should be considered alongside the objective, margins, customer journey and ability to handle demand.
Understand the economics
A business should know enough about product or service economics to evaluate whether customer acquisition can be sustainable.
Allow room for learning
Testing may be necessary to understand messages, audiences and customer responses.
Do not ignore the rest of the system
Budget is only one part of marketing. Website quality, sales handling and offer clarity can also influence outcomes.