Less than their budget. Because you're not fighting their fight. National players bid broadly and generically; you win by being surgical: exact neighborhoods, specific services, emergency terms, and message match so tight that Google's relevance pricing works in your favor.
The auction rewards relevance, not just wallets: a focused local ad with a matched landing page can pay less per click than a chain's generic ad on the same search. Their scale is also their weakness. They can't mention your town's permit quirks or answer the phone in one ring.
Practical floor: enough daily budget for 5–10 clicks in your niche (use real CPCs, not hopes). Below that, narrow the geography or the service until the math works. A tiny budget dominating one suburb beats it evaporating across a metro.