you have to consider that the first two search results gets 70 percent of the clicks in search engines… by the sound of things i’m assuming you are looking to hire an seo expert

what you should aim to do is become number 1 in 5 to 10 keywords at first. To find which keywords gets the most visits go to http://www.seobook.com .. type in your keyword and it will give you daily search estimates for your keywords.. try stay away from competitive keywords and choose long-tail keywords

but if your content is out of this world and relevant… getting a million visitors to your site is feasible