How much to charge for a re-posting of a video? Created a short promotional video for a client, it's an online magazine. 

For the sake of example, let's say I charged the magazine $700. The video is embedded into the magazine using a proprietary method (ie: not youtube, vimeo, or any other video sharing site with embed options). This is fine.

Now the video happens to be something of an pseudo-official biography on a local artist (hes in it, he talks in it, official interview stuff), but the video wasn't made FOR him, but now he's inquiring how much it would cost him to embed the video on HIS site as well, for marketing purposes. 

Again, lets say I charged the Magazine $700 (2.5min video), how much should I charge for a re-embed? 

(ps: I own the copyrights)
That is completely up to you, how much is it worth to you, etc.  Keeping in mind you have to do zero additional work on it to give it to him, and if he were to put it up on his site without your knowledge you would loose nothing.