The answer is that there are so many different variables involved, that it is impossible to give you an accurate answer. Each genre is different, and there is a wide range of differences even in the same genre.
I think the right answer would be "a text link on a site's home page" A text link from a homepage means you will get a sitewide link. Every page of that site will consists of your link. It simply means the pages the website has the number of backlinks your website will gain.
TS, link price depends on many parameters: homepage PR number of Yahoo backlinks to website domain age webpage PR is webpage indexed by Google etc... So just telling a standard price is a pure speculation
The internet isn't for sale. When you try and buy a spot in it your paying to eventually have your rankings go up in smoke. Sellers tend to be greedy and they sell to sites you want nowhere near 20 clicks of your site.
A single link can range from as little as $1 per year up to $500/month and beyond. There is no minimum and maximum.
Typically the more authoritative and/or the higher the PR of the site selling the link, the more the link costs. For example, you might spend $500/month for a single link from somewhere like the New York Post... $100/month maybe for a single link from a site like Bob Villa's... $5 per month for a link from Bob's Blueberry Farm blog... I think you get my drift. It varies drastically.
NOTE The above are ONLY for example purposes. Not saying any or all of those actually sell links. :)