Looking for a fisheye lense for my new nikon d3100?

What are my options for as cheap as possible?
(i know ill probs have to spend at least 50 bucks)

i'm not looking for one that takes pictures with a circle around it like this:

i'm looking for one the just fisheyes a normal photo like this.

You'll spend a lot more than $50 if you want decent results.

Samyang/Rokinon/Bower (same lens, different labels) do an 8mm f3.5 fisheye for around $300 - be sure to get the, 'Chipped,' version if you want metering. It's manual focus only, but you'll pay four times as much for anything better.

The fisheye lenses with a circular photo - the one you do not like - are called "circular" fisheye lenses.

The fisheye lenses without a circle - the one you want - are called "diagonal" fisheye lenses.

The el-cheapo lens adapters (that screw onto the front of your existing lens) are for the most part all circular fisheyes.

The Nikon 10.5mm f/2.8 fisheye is a diagonal fisheye, but it costs almost $800, and it will not autofocus on your camera as it requires an in-camera focus motor. To my knowledge, this is the only DX-G lens that is also an AF (not AF-S) lens.

Sigma does make some less expensive fisheye lenses (still $650 or more), and they make both circular and diagonal types - so make sure you buy the diagonal version.

Samyang/Rokinon/Bower do make fisheye lenses as well, but also - they are made in both circular and diagonal versions, and they are generally low quality. You get what you pay for.

I own the Nikon 10-5mm f/2.8. Here is a review on that lens:

http://www.althephoto.com/lenses/fisheye.php