SEO Question: I wanted to know the value of a PageRank 7 link on a science site. Does the website topic matter? What should I consider paying?
Answer:
Calculating an Exact Cost:
Yes the topic does matter, for a variety of reasons, but you can't look just at the PageRank score to get a real approximation of value. There are many criteria to consider beyond PageRank when renting or buying a link to aid in building your link profile.
You can pull out a calculator to estimate a cost range, but realistically you have to factor in a lot of ideas including your market exposure, competition, risk tolerance, and ease of link acquisition into your price. As a baseline Text Link Ads offers a link value calculator, which provides estimates based on the number of sold links on the page and the link location.
If you can get in context links from highly on topic pages (especially from trusted topical authorities) they may be worth a premium over the prices free tools estimate, even if the page itself does not have much PageRank.
Topical Integration Into the Web:
Science tends to be one of the industries that is well represented on the web, so it is not tough for a science website to get a PageRank of 6 or 7. In some niche industries that are not well integrated into the authoritative parts of the web, like porn, a PR4 may be the equivalent of a PR 7.
One of my friends has a 22 page website with under 1,000 links that gets roughly 30% of the traffic of a 6 year old 1,000+ page site with 500 .edu links and 15,000+ other links. Knowing what is needed to compete and how much competition there is in a marketplace is important for determining the value of any link.
Not only does the amount of traffic matter, but also the ease of monetization and value per vistor.
Off Topic Link Rental Risks:
If you buy more link equity than what is needed, especially if it is from high power off topic sites that poses a risk that your site might get nuked for spamming unless you have built up many other signs of quality during your site's history.
If a site sells off topic, that not only adds risk that your site might be penalized for spamming, but it also greatly increases the chance that algorithms or search editors will notice that they are selling PageRank, and cut their ability to transfer PageRank. They may still sell links, but there is no guarantee those links will pass link weight.
Search Algorithms & Natural Market Forces:
If a link opportunity is free or cheap and off topic then natural market forces AND reaction from the search engines are going to push the value of the link toward its price. The higher the authority of the PageRank source site the greater the likelihood of an automated or manual relevancy review catching the link buy.
High PageRank sites that sell way off topic put your page into a bad web community. At a minimum, it is best to ensure that the site selling you the link is not and will not sell links to spammy sites or sites which are far off topic, especially if you are buying a link exclusively for Google PageRank.
If you are buying slightly off topic it is better if the link is in the form of an event sponsorship or some other form of sponsorship that eventually is closed off to the competiton.
Direct Traffic & Secondary Citations:
If a link is highly trusted, like from an industry organization or trusted industry magazine, it may lead to direct sales or secondary citations. Plus if you buy on topic links from sources with editorial guidelines there is little risk to the link having significant downside potential. Consider the credibility effects and things outside of direct SEO value when buying a link.
Diversity of Link Sources:
If most of your authority comes from one or few sites that can look like an unnatural pattern, and there is no guarantee that any link will count, so you want to diversify your link sources if you can. For example, buying a link from the Yahoo! Directory offers little to no risk and provides great co-cition data. If you have a diverse link profile and a top link is wiped out in a future update you don't have to worry about checking your rankings to see your site drop, as your diverse link profile will keep your site ranking.
Other Market Opportunities:
Many markets have significant market opportunities which make it cheaper to create things that people will link at than to buy links outright. Many of the tools on my site have got hundreds or thousands of free links. The same can be said for many of my blog posts.
When buying junk links, it can cost anywhere from a couple dollars to $50 each, so it would cost hundreds of thousands of dollars to try to buy all the links this site has got. And you couldn't buy all of them if you wanted to because there are only a limited number of clean link sources that sell links, and a link which comes from an editorial endorsement is going to be worth more than a bought link anyway.
A site which lacks significant authority and has to buy authority is probably going to lose out toe the competiton if competing sites capture ideas that create self reinforcing market positions. Make sure you bake some of those market oriented ideas into your marketing before aggressively spending renting signals of trust / quality / authority.