The notification mechanisms such as routing alerts for start, success or failure events via email, Slack, MS Teams, PagerDuty or generic webhooks are included as part of the native orchestration feature set at no additional charge currently.

Databricks bills strictly for the compute resources (DBUs and underlying cloud infrastructure) that the job tasks actually consume while executing. The control plane handles the scheduling, orchestration and firing off of these alerts. The official documentation omits any mention of billing because there is none currently. 

While Databricks won't charge you to send the notification, downstream services (PagerDuty or custom webhook listeners) might have their own ingestion limits or API costs. You can audit the billing tables with the jobs system tables in the system.lakeflow schema to find what a job is costing you.