opensearch or elasticsearch 8.2

we need to collect all our infrastructure logs in our datacenter.

like fortigate, cisco, vmware, windows servers , linux machines. netapp , nginx, postfix

what should we use ?

we had Splunk but it was very expansive.

we want to move to free tool like ELK.

if we only use ElasticSearch internally is it free to use all his features like opensearch ?

does it has free Alerts and security features like opensearch out of the box?