I did my trekking in Uganda. It is $350 if you go during the right time of year. My group had 8 people, but I did not find the viewing angles limited. The only limitation with a bigger group is that you may be affected is someone is not physically capable of trekking to a remote spot. The gorillas are not in plain view, the scouts will tell you where they are.

"you are constantly in the hands of Virunga vehicles/lodging/guards"

I simply do not want to travel that way. :) Reminds me of being in South Africa. Very safe, provided you stay within your compound with high walls and electric fencing! The behind the scenes does sound amazing.