Hi
Free tools are better but they are not meant to be plug and play. You have to work on it as code level, that´s the problem with free tools. If you are a programmer, or you have a programmer on your team you can do whatever you want, the code skill is the limit. The problem is that if your programmer leave the company, you may get in the situation where no one can fix or change. That´s why paid tools fits better for most enterprise out there.
One example of a very good free tool is Zabbix. But there are plenty out there. e
