21.3Cost Reasoning at Scale

Absolute per-test costs depend on your model, provider, and page complexity — any table of dollar figures you read (including in this guide's earlier editions) goes stale in months. The durable reasoning:

• The ratio is what matters: Microsoft benchmarks the CLI path at 4x fewer tokens than MCP for a typical task (27k vs ~114k), trending toward 10x on long sessions. Whatever your per-token price, that ratio compounds across every test, every run, every day.
• Token spend is a first-class metric: track cost per test and per suite alongside pass rate. A cost spike usually means an agent is stuck in a rediscovery loop — it's a quality signal, not just a budget one.
• Vision-based approaches cost per look: tools that screenshot-and-reason on every interaction multiply model calls. Reserve them for UI that structural approaches can't handle.
• The build-vs-buy line: commercial agentic platforms (testRigor, mabl, KaneAI, Applitools, Testim, Functionize) bundle the token costs into their subscription. If your team lacks agent-infrastructure appetite, their pricing can beat DIY — do the math on your actual run volume.