When it comes to buying text links, beauty and value is definitely in the eye of the beholder. Some people foolishly only look at PR, while others look at relevance and traffic when placing a value on the links they buy. LinkAdage recommends that you find links that will bring you traffic and are relevant to your site. This will give you the double benefit of traffic and link popularity.
A highly relevant link on PR5 may be worth $200 per month to one person, while that same link may only be worth $10 or $20 dollars to a webmaster with a less relevant site. As the search engines are getting better at determining on-page relevancy, text link relevance will continue to become the most important factor to consider when purchasing text links.
The days of slamming 1,000s of new links at your website and getting in the top ten are long gone with the advent of the Google sandbox and algo tweaks that look for link addition patterns that tip the hat on massive link buying.
The key today is to make your link campaign look natural. This means, increase total links by no more than 20% per month and keeping your new links on relevant as possible.

Natural Linking Guide

Limit Run of Site link purchases;

Don’t go from 10 backlinks to 10,000 backlinks in one month – follow the 20% rule;

Keep all link purchases in the general category of your website;

Add strong content, free tools etc... that will encourage people to link to you;

Do some link trading but don’t over do it 500 solid link trades are better then 5000 link trades;

Keep your links long term. The longer a link points to your site the greater its value;

And the golden rule when it comes to text link is moderation. Think of link building as a marathon rather then a sprint.

The good news is that he who spends the most on links no longer automatically wins, it's he who aquires links most naturally who wins. The best part is going natural is the much cheaper way to SEO your website.