Don't the cheapest vents hold 200 people. Not sure of the rate but it could be free if you have your own server. I doubt they take up much resources.
The "free" Ventrilo servers are restricted to 8 clients. Providing a download link or running an outdated server is grounds for copyright infringement. Say I run a server (I do) and would like to run a Ventrilo server (I do) and would even be willing to pay a few dollars for a license (I am), I cannot because I need to be running a legitimate hosting company with a minimum 1000 client connection license. That's after they do an extensive review of my website and company to ensure that I will uphold the integrity of their brand... Not to mention their Linux client has been a
work in progress (with no beta) for years. The entire company/product is a joke.