Cost Control and Model Choice

Costs come from model use, tool subscriptions and your own review time. Model use depends on how much text goes in and out, and how many steps the agent takes. Prices change often, so check the provider's current price page and date your numbers.

The people, companies and numbers in this lesson are made up. Check any figure against your own situation before you rely on it.

The Cost Formula

• Cost of one run = (input tokens x input price) + (output tokens x output price) + tool calls.
• A token is a small piece of text, roughly three quarters of a word in English.
• Monthly cost = cost of one run x runs per month, plus subscriptions.

A Worked Example (Made-Up Prices)

• Assume the made-up prices of 3 per million input tokens and 15 per million output tokens.
• One run reads 6,000 tokens and writes 800.
• Input: 6,000 / 1,000,000 x 3 = 0.018. Output: 800 / 1,000,000 x 15 = 0.012. Total 0.03 per run.
• At 200 runs a month that's 6 for the model. Your review time at 3 minutes a run is 10 hours, which is far more than the model cost.

What This Shows

For many small jobs, review time dominates the model bill. Spend effort on making review fast before you spend it on shaving model cost.

Model Choice

• Use a stronger model for steps that need judgment, such as flagging unusual items.
• Use a cheaper model for routine steps, such as sorting and formatting.
• Test the cheaper model on your six-input table before you switch. Keep it only if it passes.

Ways to Keep Costs Down

• Give the agent only the documents it needs.
• Cap the number of steps and set a stop rule.
• Cache results you reuse.
• Review monthly cost against time saved.

Common Mistakes

• Switching to a cheap model without rerunning the tests. Fix: rerun all six inputs.
• No step cap, so a loop runs up cost. Fix: set a maximum and an alert.
• Ignoring your own time. Fix: include review minutes in the cost.

Exercise

• Estimate tokens for one run of your agent, using real current prices you looked up and dated.
• Compute monthly cost and compare it with the value of time saved.
• Pass condition: a per-run cost, a monthly cost, a break-even in months (see Cost Worked Example and Break-Even) and a dated price source.