Every business asking this question wants a specific dollar figure, and the honest answer depends on the trade, the market, and the cost per click in that specific category. What's more useful than a universal number is understanding the floor below which a budget can't really function.
Why there's a practical minimum
Paid ad platforms need a certain volume of clicks and conversions to optimize effectively and to give you enough data to judge what's working. A budget so small it only generates a handful of clicks a month isn't really being tested; it's barely running.
Cost per click varies enormously by trade
Highly competitive categories like personal injury law or emergency plumbing can have a cost per click many times higher than a less competitive local service. This is exactly why a specific dollar figure without knowing the trade and market isn't very useful.
Start with a test budget, not a permanent one
A reasonable approach is committing to a modest budget for a defined test period, long enough to gather real data (often a month or more), rather than either overcommitting immediately or underfunding it so thin it never gets a fair test.
Budget for the landing page too, not just the clicks
Ad spend that lands on a page that isn't built to convert is money spent proving the wrong thing. Part of a realistic ad budget conversation includes whether the destination page is actually ready. See what is a landing page, and why does ad traffic need one?
Track cost per lead, not just total spend
The number that actually matters isn't how much was spent, it's how much each real lead cost, and whether that number makes sense against what a customer is worth to the business. See tracking ROI on paid ads without a marketing degree.
Questions
Is it better to start small or go all in?
Start with a defined, honest test budget rather than either extreme. A budget too small to gather data wastes the test; an all-in budget with no data yet risks wasting money at scale.
Should the budget change seasonally?
For seasonal trades, yes, it often makes sense to increase spend ahead of and during peak season and pull back during the slow season, once there's enough historical data to know when those actually are.
How do I know when to increase the budget?
Once a campaign is consistently producing leads at a cost that makes sense for the business, and you have more capacity to take on work, increasing spend on a proven campaign is a reasonable next step.