We all know it's really hard to get good pricing and cost information.
Please share what you can so you can help your peers.
Zero cost for the core edition but you need to know linux based apps configuration a=in general but in this case the installation and configuration guides make things a lot easy . A bit of patience and clear thinking you may end up doing a lot more in your setup than you expected !!!!
Nagios Core is free to use.
The Nagios Core (PNP4Nagios + Core) is free and can be setup by Netadmin within a few hours. The only additional cost is the cloud server.