Hiya, I had that problem previously, because I had some affiliate sites that were costing me a fortune on Google Adwords, but not ranking highly on Google Organic Search. Until I happened across this Internet Gurus website, Mark Ling (
http://www.marklingseo.com/ ) detailing his tricks for getting massive organic traffic, which is free. I tried it, and all my sites have never looked back since. I just now only run Google Adwords for new products. It might work for you too.