How do you actually calculate TCO when you're managing fifteen AI model subscriptions plus a BPM platform?

My company is in this messy situation right now. We’ve got Camunda for workflow orchestration, plus individual subscriptions to OpenAI, Anthropic, Google’s model APIs, and a few others because different teams needed different capabilities and nobody coordinated.

Finance wants a real TCO model for next year’s budget. It’s a nightmare to track because:

  • Camunda bills monthly, but usage-based AI services fluctuate wildly
  • We’re probably overspending on AI models because we don’t have visibility into who’s using what
  • Some teams have unused credits sitting around
  • Integration costs with developers managing API keys and authentication across everything
  • Support costs for troubleshooting across multiple platforms

I’m trying to build a model that accounts for licensing, infrastructure, personnel (developer time managing integrations), and hidden costs like API monitoring and security overhead.

Has anyone actually mapped this out for a real environment? What costs surprised you when you did the full accounting? And more importantly, what does simplifying this look like—is it even worth consolidating?