I was paying $20/month for ChatGPT Plus and considering Notion AI Business ($20/user/month) to get the workspace-aware AI features. Then I did the math: Notion's API is free, OpenAI's gpt-4o-mini is $0.15 per million input tokens, and my actual usage is ~5,000 input tokens per query. That's $0.00075 per "ask your notes" call. Even at 100 queries a month, I'd spend less than a dollar in API costs. This is the build-vs-buy take the SaaS comparison sites won't write. Below is the 50-line implementation, the real token math, where the DIY approach breaks down, and when to just pay the $20. For the SMB-perspective comparison (no code, full pricing breakdown, the 2025-2026 Notion AI restructuring), the full version of this article covers the non-developer angle. The build-it-yourself stack Three pieces: Notion API for the data layer — read your pages and their content. Free, well-documented, rate-limited at ~3 req/sec. OpenAI API (or Anthropic) for the AI layer — send your notes as context, get answers.…