Good prime lens for my budget and shooting?

Hey guys i'm looking for a decent prime lens for around 300-400$, Used, new doesn't matter.
i'm currently shooting on a nikon d3100. I love to shoot landscapes, portraits, and occasionally video.

A good prime is the AF-S DX 35mm f/1.8, the new AF-S DX 40mm f/2.8 macro, or the AF-S 50mm f/1.8, all well within your budget. They are $200 to $300 new. Don't buy a used one, you will only save a few pennies as they have a high resale, so you might as well get the 5 year warranty.

The 35mm will work better for landscape and the 50mm better for portraiture (but no need to buy both).

http://www.althephoto.com

For portraits the AF-S 50 mm f/1.8

Landscapes require some kind of wide angle lens, but the prime 14 mm lens costs in excess of $1, 890

There are no other prime wide angle lenses you can use on your D3100.

The 18-55 mm lens will shoot good landscapes if you are up to the task.

The other alternative, the AF-S 10-24 mm will produce brilliant landscapes but again exceeds your budget, they cost in excess of $800

For landscapes, a lot of different focal lengths could be best. Some say wide angle, and that sometimes works, but it can turn mountains into molehills, and if the foreground and sky are not interesting you will have plenty of it.
If you want to do potraits you want at least some telephoto.
I think this points to the 50mm f1.8 AF-S.

As the first poster said, the 35mm AF-S is great. Just get that one.