A Client Asked Me to Add AI. I Spent 2 Weeks Researching the Costs. Here's What I Found.

The math that changed how I think about AI features

The Request

A client messaged me about adding ChatGPT to their invoicing app:

"Can we add AI to help users write invoice descriptions? Budget is $15K."

They have 500 users paying $20/month. Seemed straightforward.

I started prototyping. The code was simple:

const response = await openai.chat.completions.create({

  model: "gpt-4",

  messages: [{ role: "user", content: userPrompt }]

});

But before quoting, I decided to calculate the real long-term costs. What I found surprised me.

The Research

I spent two weeks diving into AI economics. Not because I'm some expert, but because I couldn't find clear information anywhere about what it actually costs to run AI features at scale.

Quick note: I built a simple calculator while researching this. If you want to run your own numbers:

👉

Input your numbers:

• User count


• Expected usage


• Model choice

Get realistic estimates:

• Monthly/annual costs


• Infrastructure needs


• Margin impact


• Sustainability warnings

Takes 2 minutes. Might save you from expensive mistakes.

Additional Resources

I'm working on a more complete guide for managing client projects (contracts, budgets, security checklists, etc.). It'll be ready soon. Want me to share it when it's done? Drop a comment or follow me here.

Your Experience?

Have you built AI features? What surprised you about the costs?

Are you considering adding AI? What questions do you have?

Let me know in the comments.

Note: I'm @arbythecoder on most platforms. I write about software development, Devops, client work, and the honest economics behind tech decisions. All the numbers in this article are based on publicly available data and standard API pricing as of November 2025.

Tags: #ai #webdev #openai #costs #saas #cloudcosts #gpt4