The most cost effective method is to Google the words SEO Search Engine Optimization and spend about a month reading everything you can.
Create a Webmaster account on Google and digest all of the stats they're giving you, all the links they're giving you -- not just what the information is but why is it important to Google.
Do it yourself is the best appoach.
Do not believe ANYTHING you read on this board about SEO, including this
Kesey