Hey there guys. My wife's birthday is in 2 weeks. It also happens to be mother's day. Double Whammy for me

Anyway, I bought her a Nikon D5100 a couple years ago. She loves it, but really only uses to take family photos and such. That being said, she has said for awhile she would really like a fisheye lens.
Most of the fisheye lenses I've found are extremely expensive. Being that she is not a "photographer" I find it hard to stomach a $800 lens. I'd prefer to spend 200-300... possibly a little more if necassary... to get her something that she can get the fisheye effect, and have fun with but won't be a complete waste of money if she ends up using it a handful of times and never going back.
Any advice would be awesome!
Thanks