Effective August 1st, 2019, AWS Config rules will switch to a new pay-per-use pricing model, lowering the bill for almost all existing AWS Config rules customers. AWS Config helps you assess and maintain compliance over your AWS resource configurations. You can use AWS Config rules to view compliance history and trends, identify configuration drift, and remediate configurations that fall out of compliance. Today, AWS Config rules are priced based on the number of active AWS Config rules you have in your account. An active rule is defined as a rule that records a compliance result against at least one resource during the month. In the new pricing model, you will be charged based on your monthly AWS Config rule evaluations. A rule evaluation is recorded every time you compare your resource configuration against the rule. This better aligns with your actual usage of AWS Config rules as your charges are based on the frequency and the number of resources evaluated. The new pricing delivers value by supporting volume usage, giving you more control of the AWS Config rule cost in your account. Tiered pricing makes it more affordable than ever to implement configuration compliance within your AWS environment, for as little as $0.0005 per rule evaluation. This new pricing is designed to provide almost all of the current AWS Config rules customers with a significant reduction in their AWS Config rules bill.

from Recent Announcements https://aws.amazon.com/about-aws/whats-new/2019/05/announcing-the-new-pricing-plan-for-aws-config-rules/