Like Trist suggested, Decimation Master would more than likely produce a bad result for something that needs to be animated. It’s mess of triangles could even produce something that’s not ideally optimized for realtime rendering either. You’d be better off keeping the subdivision levels pretty low to begin with, and retopologize manually.
It could depend on the client’s goals, but with a budget of 1000 polys (especially if they mean triangles) and an engine like Unity, there’s a good chance they’re aiming for something that ends up in a mobile application. Depending on other factors, there’s a chance normal maps might not even be utilized. Even still zbrush should be able to handle the modeling, UVing, and projection painting required.
There is a beauty in low poly works that can be far from pointless exercises. Aside from still being required for some systems and game genres, it gets you in the habit of being efficient, really gets you to focus on the major planes and silhouette of the model, and also requires some good painting if it comes down to a color map only.