Plugin to automatically insert link and anchor text

Hi,
I have a blog which currently has around 500 articles. There are no adverts and it has been very much a labour of love.

In order to rationalise the time and expense however just recently I have had the idea that at the bottom of every article there could be a quick link with some anchor text to a specific page on another website that I have which provides my livelihood.

I’m not talking anything elaborate; just one link per posting which in turn takes the user to a specific product on the other site. I don’t really want the same text at the bottom of every article; perhaps if I were to select say ten products, write ten descriptions (and anchor text) and then have one inserted at random at the end of each post.

Does anybody know of a plug-in or tool that will allow me to achieve this or would it be a case of manually editing every post at all the link text and code manually?

Thanks for your help.