First, I recommend digital. Hoardes of pictures are always fun to do with Cosplay photography =)
If you get a mid-range digital compact camera, say $300 CAD or so, I think a person would be able to take pictures at the level of, or higher, than probably 85% of the cosplay pictures you see online.
Like most equipment (camera, sports, etc), I recommend going a little cheaper on the first purchase. That lets you figure out how much deeper into the field you'd like to go. More specifically, it helps you figure out what you need in a camera, rather than some generic salesperson.