Goose,
Yeah, like most anything else, covers come in all different styles and price ranges. Believe it or not, but the one I went with is only mid-range. I've seen some that are much more expensive. It all depends on what kind you need and what's best for you. I needed an all weather for the elements but some folks have garages and prefer an interior cover for the dust.
You just have to decide what your needs are and then start looking on google for the cover that's right for you. I would recommend getting a custom fitted cover though since the 300C is kind of a monster and something with a nice lining that won't harm the paint. Covercraft makes some good ones and they do custom fitting as well. Try this link:
http://www.carcoverworld.com/Frames....stom.asp?CID=1
Good luck!