Is this what you're looking for?

http://cgi.ebay.com/42x-HD-Fisheye-F...QQcmdZViewItem

I'm with Brent. For an inexpensive fisheye, you really can't go wrong with the Zenitar. I have never used the "filter" type, but like most things, you get what you pay for, and I wouldn't count on a $35 filter producing great results.