Where can i buy a descent fisheye?

I own a Nikon D3100 and i want to buy a fisheye in order to film people skating but they are all really expensive. I understand that they are expensive due to the quality so i want to know where can i buy a descent fisheye that won't cost me more than a $100 and at the same time works pretty well.

Added (1). Edit: I'm sorry, i forgot to mention that i was looking for the type of fisheye lens that is put in front of another lense.

You can find inexpensive fisheye lenses on Amazon.

Here is one

http://www.amazon.com/...B002LTWDSK

This is one of the inexpensive one.

Nikon makes a 10.5 mm fisheye

http://www.nikonusa.com/...8G-ED.html

And Sigma makes a fisheye used on full frame cameras like the Nikon D3 or D4

http://www.sigmaphoto.com/...heye-sigma

As you can see, you budget is a little low at $100.

For clarity, you will be using the video feature on the D3100 since it does not use any kind of film

The $100 price will only get you a fisheye lens/filter - one that goes on the front of your lens. You will probably not like the quality of that solution.

I like the lomo fisheye. Cost around 20 bucks because it has distortions… I mean, its 20 bucks. That's awesome. And distortions are part of the glory!