Do health check requests coming from the ELB cost money?

I have an application load balancer that routes traffic to two EC2 instances in a target group. The application load balancer periodically checks the availability of the EC2 instances by doing a health check. It makes a request to a healthcheck endpoint and when it gets status code 200 it knows the instance is still functioning.

The default interval for these healthchecks is 30 seconds, but i thought that was a bit too long so i've set the health check interval to 5 seconds instead. This made me wonder; do these health checks cost money? Is it more expensive to do health checks every 5 seconds as opposed to the default 30 seconds? I would also like to know what the optimal healthcheck interval would be when processing requests for a social media website.

Thanks