Photo copyright advice

[craig_allan]

I've just received the following email:

Hi Craig,

I am interested in purchasing a high resolution of your photo as posted on
flickr.com. The photo is entitled Frosty Road. I would like to buy the
image as royalty free for use across a variety of media.

Can you please advise the cost for purchasing this image from you? If you'd
like to chat about this on the phone, please don't hesitate to ring me on ***********.

I've got two photos on Flickr called Frosty Road:
http://www.flickr.com/photos/craigallan/91532447/
http://www.flickr.com/photos/craigallan/91532445/

This is the first time this has happened to me, so can anyone offer any advice? There was a link to this website in the signature, which looks genuine enough.

Should I allow him buy the image royalty free, or something else? How much would be reasonable to charge for this kind of thing?

Thanks!

x-posted