How much does a link worth?
If you’re a webmaster you probably know that SEO worth money. One of the main aspects of SEO is incoming links. One of the key elements of a site ranking in search engines is the links other websites send to that website.
For incoming links webmasters have developed several methods to gain more incoming links:
1. Link Directory - A directory which contains categories and a webmaster can add his website with details under the relevant category. Recently search engines discovered the use of directories and reconsidered the importance of them as an SEO factor yet, they are still relevant.
2. Buying links - You can pay other websites for an incoming link for your website. Then you can see other websites with links on the bottom or in other places promoting irrelevant content.
3. Buying Domains - People tend to buy domains and build a network of websites which correctly link to each other and by doing so help with the ranking.
Of course there are other factors to consider as page rank (Google’s Page Rank) and traffic ranking.
4. Gadgets, Gimmicks and so on - People use different methods to cause people to intentionally or non intentionally place a link on their website - this is called link baiting and i personally know of some websites which were disqualified for this - but it still works 
So how much does a link worth?
That depends. It depends on the relevancy of the website - for example a website about barbie dolls linking to a gambling website (irrelevant) unlike a website about finance linking to an how to make money website
Other than the relevance, there’s the page rank and the traffic rank and the time that website exists and other factors.
Some links can be worth even $500, so consider the link industry as another source to make money