I wired an AI code reviewer into CI, felt clever, and then looked at the bill after a busy week of PRs. Every push, every commit, sending full diffs to a big frontier model. It added up faster than I expected, and most of what it was reviewing was formatting changes and README edits that did not need a genius reading them. So I rebuilt it as two tiers, and the cost dropped hard without losing the catches that mattered. The idea is simple. Do not send everything to the expensive model. Use a c...