most PPC search engines will give you % and let you put a search box on your site. Check out
www.kanoodle.com
www.7search.com and such. There is one that combines all the PPC results into one and pays you a higher ratio. If I can remember it, I will shoot you the URL in this thread. The person who ran/worked for them used to post here and it was in their sig.
ZoiNk