I had a company recently contact me asking if I would consider selling a link from a recent product write-up I wrote to their on-line store (that sells that product). I have never heard of selling links before and don't know much about it. Does anyone do this? How much? Thanks.
That being said, if you choose to sell links, pricing depends on your traffic and page rank - and what your client would want to pay.
Also, you may want to check out Sponzai, from Izea, the Pay Per Post people. You can earn money selling links, and a nice feature is that they figure out what a link sale is worth on your blog. This in turn will help you price links that you sell independently.