Yacht Jennifer just visited Fernando de Noronha and posted about the place and the fees. Not cheap for foreign yachts!....
from the blog:
"Up till recently cruisers could not visit Fernando unless they had cleared into Brazil before, but that has now changed. The costs for visiting yachts are steep though, almost USD 100/day for the boat and a landing fee plus a park fee of USD 35/day/person."
Personally, I think there is much more to see and enjoy on the mainland, and no fees there too.