SEM for travel site

Our site [login to view URL] has established since 2005 which provide travel information and tour package in Vietnam. We has good page rank and average traffic from search engine. Now what we want is a professional web marketing team that could help us achieve more from search engine traffic and as well as promotion the website. Increasing targeted traffic is the main goal, beside we need a guaranteed rank from search engine for some of our target keywords. We prefer a flexible payment for the service as the provider need to maintain the results for us (Fixed amount when achieve goals and monthly payment) This is information of our site: [login to view URL] Language: English, Chinese Affiliate program: Post Affiliate Pro. Main targeted keyword: vietnam tour, vietnam vacation