Cant the same environment be shared by different groups/stages, as what i have posted earlier ?
the system we have currently is precisely for the reason that it might be prohibitively expensive to have separate physical environments.
like taking Jean's example: have a separate environment (paths) for A and B. Keep testing them in their little worlds on the same hardware.
we also have an application which has a dev and a test but pointing to two different ports on the same webserver instance.
Just a thought.