I built AI agents for my agency that cost almost nothing to run

Everyone talks about AI agents like they're some expensive, complex infrastructure play. I run several of them across all our D2C brands and ad platforms. The monthly cost is negligible.

Here's what they actually do:

The Fatigue Detector (runs daily)

Scans every active campaign across every brand. Checks frequency, CPM trends, CTR decay. If a creative has been running too long and its performance metrics are declining, it flags it. The flag goes to Slack. I decide whether to pause or rotate.

Before this agent, I was doing the same check manually across all our ad accounts every morning. Now it's a Slack message I read with my coffee.

The Budget Rebalancer (runs weekly)

Looks at the past week of spend and ROAS across all campaigns, all brands. Identifies which campaigns are above target ROAS with room to scale, and which ones are below target and should have their budget trimmed. Proposes a reallocation.

Key word: proposes. It doesn't move money. It sends a recommendation to Slack with the exact numbers and reasoning. I approve or modify. The human makes the final call.

The Outcome Checker (runs daily)

After the day's data is mostly settled, this agent reconciles what the ad platforms reported vs what Shopify actually saw in orders. It catches the most common lie in performance marketing: platform-reported ROAS vs true ROAS.

If Meta says a campaign did 4.2x ROAS but Shopify only shows 2.8x in attributable orders, I want to know about it before I make scaling decisions based on inflated numbers.

Why the cost is negligible

Some agents are pure rule-based. No AI model calls at all, just database queries and threshold checks. The ones that do use AI use the cheapest model that's smart enough for the job. The combined cost is less than a single team lunch.

No GPU instances. No fine-tuned models. No inference endpoints. Just well-structured prompts and queries, running on infrastructure we already had.

The whole system took about two days to build and has reclaimed significant daily hours that used to go to manual monitoring work. That's the kind of ROI I look for: build it once, run it forever.