It is recommended to configure alerts via SNS for critical findings.
While you could use 3rd party solutions such as Security Information and Event Management (SIEM) , User and Entity Behavior Analytics (UEBA), Network Behavior Anomaly detection (NBAD), and runtime monitoring solutions to analyze the sources that GuardDuty uses, the effort and cost of deploying these solutions, integrating them, and generating VPC Flow Logs on all your VPCs would represent a much higher cost and require much more effort, therefore we recommend other solutions for custom threat detections, in a later phase. Other solutions can be “wins”, but not “QuickWins”.
https://www.xmind.net/m/K3fmSB
https://aws.amazon.com/guardduty/pricing
The service has a 30-day trial period (free trial)
You can verify current usage and estimate future usage of this service.