You pay for what you get – firms offering cheap SEO are usually link-buying farms. These types of SEO firms don’t really do SEO at all – they pay a small fee for spamers to place links to your website which temporarily increases the rankings of your site. Not only does this type of SEO violate search engine guidelines, but it will actually cost you more in the long-run when your competitors find out what you are doing, report your site and you get banned from the search engines altogether.
Think about the professional rate other people charge. If the average rate for a freelance web developer was $110/hr, how much time do you think they would spend on a project that was only bringing in less than an hours worth of income? 15 minutes? 20 minutes? Remember that freelancers and businesses often have considerable expenses to pay.
Clearly, firms offering cheap SEO aren’t using qualified experts. If they are, you will only be buying a few minutes of their time per month.