ManRay 1 wrote:
Zoom Lenses are great but I have a nice stable of Primes that I love to use when the shot calls for it. One of my favorites is the Nikon 85mm f1.8. It's fast, light weight and has a beautiful soft, milky Bokeh. I found mine used, for $300. It'a a wonderful addition to your tool box.
OP has a D3100 w/o the built-in focus motor. I doubt you will be able to get a decent 85mm f1.8 af-s for under $400.