For $200, you can't buy much, but I would suggest buying a flash rather than lens. It will help you a lot.
However, a decent lens that's close to $200 is the AF-S 35mm f/1.8G if you want a shallower DOF than your kit lens. I think you can get it for $250-$280 at BNS. And since it's afs it can focus with D3000.
Good for portraits. :thumbsup: