Price difference is huge but don’t forget to take into account the time you’ll spend managing the monitoring tool, that’s a “hidden cost” easily overlooked. (However, I have almost no experience with Zabbix so I can’t tell if it’s a “turnkey” solution like PRTG)
PRTG feels old and clunky. We are getting spammed by a sensor up alert on snmp to a windows server and the sensor never goes down in the first place. The graphs are low quality. It uses so many system resources and warns you against using too many WMI or PS/Bash sensors. It struggles to guess when its overloaded and checking CPU/RAM/disk queue does nothing to help you guess. We have been needing to move from PRTG for a while.
For my needs I just want icmp, http, https, tcp, ssh. But IT requires server/switch/router resource metrics as well. Zabbix is mature, has better dashboard and graphs, has a dark theme, and very efficient with the system resources. We have multiple vendors that use it for monitoring and my friend has replaced PRTG with it for all their networks that they monitor and they look at far more than what we need to monitor. We’ve also looked at n-able but I’d prefer open source where possible.
I’m going to keep trying to get comfortable with it and when it comes to December I’m hoping we can opt to not renew our PRTG subscription.