Although Google index more than 8 billion web pages, they cannot guarantee that they will crawl all the pages on a particular site. However, Google are always working to increase the number of pages crawled and hope to include more pages in the index soon. For more information about how Google find and include pages in the index please read Google’s Technology Overview.
If your site’s internal link structure does not provide a path to all your pages, the Google robot may not see all the pages on your site. Google follows links from one page to the next, so pages that are not linked to by others may be missed.
Basically, you can’t buy your way into the actual search results. You can however, purchase advertising adjacent to Google results.
Excerpt taken from Google Webmaster Info