As Nagios Core is an open source product, you cannot earn money as a product. 

However, you can earn for Nagios Installation, Configuration  & Ongoing Support. In other words, setup cost for end-client & regular o&m support.

Other side, you can convert Nagios Core into Nagios XI by contacting nagios.com

Nagios Core costs less than SolarWinds. There are no additional costs.

The solution is expensive so pricing is rated a one out of ten. 

It's free. 

Most of the features in Nagios Core are free. Most plugins are free. 

When we look at pricing version eleven requires purchasing a license. With version seven no license was required since it was open source. When you upgraded to the licensed version only then did you pay for a license

Nagios Core is a cheap solution.

Nagios Core is an open source solution, and there are no licensing fees.

The product is open source so it's completely free. It's deployed on an Amazon server so we pay a small amount, maybe $30 per month, for the AWS hosting.

We are using the free version of Nagios Core.

You should be sure that you have the expertise to customize it, and I would recommend the paid-for Nagios XI for the additional support.

I would rate the solution's pricing an eight out of ten. 

We are using the free version.

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. 

The enterprise version has technical support. The version we are using is free.

Nagios Core is free to use.

It's free.

The only actual cost was the cost of a set of feet for the display unit that was used in the service desk area. Everything else was either end of life machinery (i.e. the server) or freeware/gnuware (openSUSE Linux, the packages themselves). There is no day-to-day cost other than the usual running cost of the server.

We are using the free version.

Nagios is open sourced, therefore there's no need for licensing.

Its free. I have not used the Enterprise version. 

There's no licensing costs, and I feel that monitoring is not essential software for a management board, at least until bad things happen then it becomes invaluable.

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 !!!!

There is no license cost, just a cost in time.

We are using the open-source, unpaid version.

We are using the free version.

I only use the free version.