For the past few years, many of the search engines (except Google) have offered a simple PFI model so you could speed up the indexing of any page of your site by paying a fee. This fee covered a year of inclusion in the search engine database plus frequent respidering of the page, if it met with the search engines' quality requirements.
Many human-edited directories have also offered PFI programs in order to list your site. For instance, if you have a business or any type of commercial site, you have to pay Yahoo $200 to them to consider your site for inclusion in their directory. Once reviewed by their editors, they would add it to the directory, and you simply have to pay a yearly fee to keep it stay there.
PFI also offers another solution to the problem of sites with dynamic URLs in that search engines may not be able to index. Because the pages using dynamic technology are often refreshed every 48 hours, they can help ensure content in the indices is up-to-dated by this way.
Paying for inclusion doesn't influence the ranking position of a website once it is included in the database. You are just paying for the search engines to spider your site's pages. That's why we can't achieve high ranking by PFI.