Fish Eye Lense Nikon D300?

I bought my daughter a camera last year Nikon D300 and she is asking for a Fish Eye lense. I'm finding Nikon lenses to be way out of my price range ($600-$900) and am looking for an off brand for about $300.

Realized when I started looking that I know absolutely nothing about cameras and after an hour of searching I'm hoping someone can guide me!

Fish Eye Lense for a Nikon D300 - what type of lense can I look for? I saw some out there brands Rokinon and Bower but I do not understand what fits to what. I was hoping to find something that said "fits D300" but no luck.

If your on a budget check out eBay, they have lens adapters that will fit.
You can get these adapters much cheaper, $30-$100.
You might be better served to get her a few different cheap adapter to play with as they all offer a different viewing angles. I put a link to a search below.