Vue is wonderful, and works great with Poser. They have sales, so keep an eye out. (I think they offered it for $99 once.) Vue 5 is coming out soon; maybe Vue 4's price will drop then.

Alternately, you could go to RuntimeDNA. Their "Microcosm" sets are pretty good for working inside Poser. Better than the Cyclorama, anyway. They also sell very nice trees of all kinds, and are always making more.

Of course, when you add it all up, it might be cheaper to just buy Vue. ;-)