Build the total before choosing a daily figure.
A campaign budget can include media, planning, creative production, a landing page and management. List those costs separately. Confirm the currency, taxes, payment timing and recurring commitments. The amount entered into an ad platform may be only one part of the expense.
Define the offer and how many additional customers the business can serve. A promotion that brings demand beyond capacity creates another problem. Timing, available stock and the team handling enquiries all belong in the budget discussion.
Use your own economics.
Consider the contribution available from a completed job or sale after its direct costs. Decide what acquisition cost the business can sustain. Historical close rates can help with a scenario when the data is reliable. Label an estimate as an estimate.
Divide the total cost by qualified enquiries to find cost per enquiry. Estimate customers using enquiries multiplied by your close-rate assumption, then divide total cost by that estimate. Treat this as a planning scenario and test several assumptions.
Understand platform pacing.
Google describes average daily budgets as an average across a month, with published spending limits. The amount spent on a particular day can vary. Read the current rules for the campaign type and account.
Agree who is authorised to change a budget, which changes require approval and how often the account is reviewed. A clear approval process is particularly important when multiple people manage campaigns.
Set a review point.
Choose what the test is meant to teach you and when it will be reviewed. Record spend, suitable enquiries and completed business outcomes where available. A small sample should be described as a small sample.
There is no single responsible budget for every business. Start a conversation with the offer, area served, available evidence and the amount you can commit. A proposal should then make the scope and costs explicit.