I'm trying to understand perspectives around Vulnerability Management (VM) scanning. Let's say you VM scan all devices in production environment, disaster recovery environment, and any machine that can connect to said environments at your office. You also work at a budget conscious company. In this scenario, would you:
...and what is your reason for why you would choose this?
Everyone is budget conscious. The answer comes down to risk acceptance.
At my company, we purchase a site-license and install the Vuln scanner on all devices to raise the bar and redirect everyone't time and attention to those risk decisions that are more business-facing. Plus it reduces time pacifying auditors.
So why not use a free open source alternative? Yes, it may not be as robust as your current VM solution, but you can use it to supplement for where you do not have licenses, also you can use it to compare.
I use both our paid solution, and the free solution. The paid solution scans our higher risk assets, and the open source solution scans all of our assets.
The open source solution
Additionally, depending on your setup, if all of your machines are using a baseline template/configuration and you don't have deviations from it, you can just scan the template and not have to worry about the licensing. But becareful with that method as it requires your machines to be exactly the same otherwise you are ignoring machines.