How important is cost estimation in system design interviews?

How important is cost estimation in system design interviews, particularly for roles that aren't specifically focused on infrastructure finance? Should I proactively bring up infrastructure costs, or wait to be asked? If it is important, what's a quick and dirty framework for ballpark estimates for cloud resources? Like, how much does a TB of storage typically cost on AWS S3 per month? Or what's a rough cost per million API calls for a simple Lambda function or an EC2 instance? Having some common numbers for compute, storage, and networking could really help frame the discussion around trade-offs.