WAF pricing: rules and rule groups

The free managed rule groups still incur a charge

Be aware that, although the AWS managed rule groups that are listed as "free" don't incur any specific extra charges, they do still incur the standard $1/month fee for each rule attached to your WAF ACL.

If you have a WAF ACL created in your account, it doesn't matter if any CloudFront distributions or any other resources are actually associated with that ACL or being used - you will incur the charges for the ACL and rules regardless.

The wording can be a bit odd on the WAF pages - this includes both custom rules you wrote yourself and any other rules of any kind, meaning an average WAF ACL is going to cost around $12/month or so in practice for the ACL cost + 7 rules.