Link buying is frowned upon, but then the Google algorithm isn’t infallible. If you buy, buy sensibly. Check out the site, see how many outbound links it already has and who it’s linking too. Also run the copy through Google search to see if it’s been lifted/used before. These are all telltale signs for Google to pickup upon and classify it as a link seller. Your site will be tarred with the same brush if you’re receiving links from it, so definitely be careful.
Also, there are some good directories out there that, for a one off fee, will provide a quality back link indefinitely. See BOTW.org especially. There is of course the holy grail of DMOZ listing…
Finally, with links you got to remember quality over quantity. It’s worth hunting down that right partner rather than spamming people for links. Consider article based link purchases rather than uncontextual text links.
Good luck and stick it out – you’ll get there!
All the best,
Aaron