Smallstep has several pricing tiers for Hosts and for Support levels based on your needs. 


         If I need to support thousands of certificates being refreshed or renewed daily, what tiers are right for me? 


Our SaaS offering runs in Google GCP in the US. We also have a run anywhere version that can be deployed on-prem.
For service mesh (or any) short-lived workloads you likely don't want/need active revocation or advanced PKI functions. We typically recommend our DevOps authority for these use cases.
We don't price by certificate, we charge by endpoint (defined here). You can use this calculator to determine a cost estimate.