Thank you requesting here and explaining your use case.
Currently we don't have the support to add IP ranges. However, we will add this enhancement to this monitor.
If you have any domain which will resolve all these IPs, you can just configure the domain name and enable "Resolve Hostname(s) on every poll" option.
Here it will be charged based on the number of IPs in that range. Every 10 IPs will consume 1 basic monitor license.