http://www.amazon.com/Opteka-Super-Angle-P...7775&sr=8-3

Opteka .38x HD² Super Wide Angle Panoramic Macro Fisheye Lens for Nikon D50 N80 N75 N65 N55 SLR

Yes, I know it's cheap. No, I don't expect high quality.

What CAN I expect? I just want something that's useable to make some fun/silly fish eye shots.

You can always search Flickr for example shots. Thats what I do when I am looking for lenses for my Canon, so that I can get an idea of the sort of results I should get.

The other thing is, there are some small example shots on the Amazon page you've linked to.

That's going to be REALLY crappy. Get the Peleng 8mm or Zenitar 16mm if you want something cheap to play with.

And where can I find them, and how much are they?

Ebay and about $175 http://cgi.ebay.com/NEW-FISHEYE-ZENITAR-N-...1QQcmdZViewItem

Yea, see, $30 is sort of "throw away" to me, where as $175 isn't. Oh well.

a 16mm f/2.8 for 175$! oh well. I'd buy the 30$ one instead.

It's not even a lens though, it's a lens attachment. So you have a whole ton of glass it's going through and half of it is dirt cheap.

Maybe it's just me, but if I had a Nikon camera (and I do) I'd not settle for less than the 10.5mm DX fisheye. It's a tad spendy, but a great lens if you plan on doing regular fisheye style shots.