The cost of the WAF rules is already extremely low so a free trial is not offered. For example if you were to run a trial for two weeks on one ALB and use 2.4 million requests your cost would be approximately $12.40.
Personal opinion just use Nginx or F5 XC distributed cloud if you need a good WAF solution for AWS as the AWS WAF engine just has limits and even with F5 rules the AWS WAF engine still is not the best 😀
