I use a 9-agent SDD harness where each phase uses a different model. The total cost is $10-15/month. Here's the full breakdown.

Background: I'm a Principal Architect working on .NET 8 microservices at scale (~600 locations, 44k articles). I got tired of burning Claude/GPT tokens on tasks that don't need frontier reasoning, so I rebuilt my entire coding workflow around Spec-Driven Development with per-phase model selection. The core insight is obvious once you see it: different phases need completely different capabilities . A phase that maps files has nothing in common with a phase that writes a formal spec. Running both on Claude O