I can't tell you what to charge, but this might help: Stock Photo Price Calculator
In case you don't have one yet, here's the text of the commercial use license that I use...
Commercial Download License
What you can do:
Photographer grants you a perpetual, non-exclusive, non-transferable, worldwide license to use this image for permitted commercial purposes, defined as:
* advertising, promotion, brochures, packaging
* as part of a commercial website for promotional purposes (maximum 800x600 pixels) use
* prints, posters, flyers, tearsheets for promotional purposes (not for resale)
* prints, posters, or other commercial display of image
* magazines, books, newspapers, other printed publications
* video, broadcast, theatrical
What you may not do:
Buyer may not resell, relicense, redistribute without express written permission from photographer. Use as a derivative work, and reselling or redistributing such derivative work is prohibited. Images may not be used in a pornographic, obscene, illegal, immoral, libelous or defamatory manner. Images may not be incorporated into trademarks, logos, or service marks. Image may not be made available for download.
Photographer retains all rights, license, copyright, title and ownership of the image(s).
There is no warranty, express or implied, with the purchase of this digital image file. The photographer will not be liable for any claims, or incidental, consequential or other damages arising out of this license or buyer's use of the image(s).