This document explains Google Cloud Armor pricing details.
|Google Cloud Armor Price|
|Per Policy Charge||$5 per Google Cloud Armor security policy per month|
|Per Rule Charge||$1 per rule per month, pro-rated to the day|
|Incoming Requests Charge||$0.75 per million HTTP(S) requests|
If a backend service has a Cloud Armor policy associated with it, you can use the user-defined request headers feature with that backend service without any additional charge for the user-defined request headers feature.
Promotion: Until Dec 31, 2019, your queries per month charges across all projects in a billing account are capped at $500.
If you pay in a currency other than USD, the prices listed in your currency on Cloud Platform SKUs apply.