> I suppose it depends on how you are using it, but for coding isn't output cost more relevant than input - requirements in, code out ?

Depends on what you're doing, but for modifying an existing project (rather than greenfield), input tokens >> output tokens in my experience.

Unless you're working on a small greenfield project, you'll usually have 10s-100s of thousands of relevant words (~tokens) of relevant code in context for every query, vs a few hundred words of changes being output per query. Because most changes to an existing project are relatively small in scope.