i was online earlier and came across this little beauty available at Freestyle Photographic Supplies now:

it's a holga fisheye lens that apparently is made entirely of plastic. now i know there is already another fisheye lens available for holgas, the thing is that this beautiful piece of plastic will only set you back $25 (versus about $70 for the other one). you can check it out here for more details. here's a shot Freestyle provides
