How much to charge for single print?
 

I always hear from "pros" that us weekend warriors are uninformed and don't know what to charge, so I'm going to ask. I got this e-mail:

I really like the "color of sound" photo you posted on your site on Nov 11 and would like to get a big printout of it. I am not sure if you are selling those or if you can share a digital file, but it would be awesome to hear from you if there is a way I can get it. I have a perfect place for it already!!!

First off, I'm not giving the digital file so let's not talk about that. What I'd like to discuss is:

1. How much should I charge over printing costs?
2. Best place to get larger prints from.

I have a general idea, but am always welcome to consider other people's thoughts. The photo in question is:

<a href="http://www.flickr.com/photos/9899098@N04/4094470768/" title="The Color Of Sound by photoboothguy, on Flickr"><img src="http://farm3.static.flickr.com/2766/4094470768_36760a8c9e.jpg" width="500" height="333" alt="The Color Of Sound" /></a>