Personally, i have never bought any links and for a good reason.
A.) You often don't know where they are going to be placed and directory submissions are left to someone else SEO judgement.
B.) People often sell, for example, "1000 Backlinks" and they will be placed in link farms and websites that google recognize as "Blackhat SEO" sites.
You are far better justing perservering and keep on blogging, posting your link on forums, writing press releases, submitting to directories, exchanging links with similar websites and so on.
It can take a long time, but if your links are of a better quality than the sites above you in search results(because they bought their links) you will soon overtake them.