I would napkin math the averaged cost per-review to be less than $1, which is less than our most rigorous validation pathway in CI (needs GPU for up to an hour). Time-wise around ~10-15m, with variability - and a bug in Argo with pod scheduling delays. This is fine because developers check in on their own PRs when they do and then make the changes that are needed. A key point here is that we are keeping humans in the loop in the PR.
This is a large monorepo, I would expect much lower numbers for polyrepo setups.