According To Webopedia:

In search engine optimization, on-page optimization refers to factors that have an effect on your Web site or Web page listing in natural search results. These factors are controlled by you or by coding on your page. Examples of on-page optimization include actual HTML code, meta tags, keyword placement and keyword density.

In search engine optimization, off-page optimization refers to factors that have an effect on your Web site or Web page listing in natural search results. These factors are off-site in that they are not controlled by you or the coding on your page. Examples of off-page optimization include things such as link popularity and page rank.

Whether it’s an existing site or a new website, we have to follow the basics. Proper Title Tags, Meta Tag Descriptions, H1-H2 Tags, keyword density, externalizing CSS, proper code to text ratios, lots of appropriate content and then white hat techniques involving article develpment, submissions to blogs, forums, rss feeds and much more…

Again, we have been able to do it for ourselves as well as our clients. Experience is everything then cost. If you are considering other companies that’s great but ask them one simple question, “Are they ranked on the #1 page of Google for a popular and appropriate search term phrase?” If they are not, no excuse is acceptable