Hello, Jamie! Welcome to Oprano!
You best know the categories into which your pic falls with regards to niche, photographer, models, etc. The advice you've been given so far is very good. Check out and see what the competition - your direct competitors - are charging. Being new and trying to break into the business, you'd probably start out charging less.
Two other suggestions: one, is I want to emphasize again how important all the required 2257 documents on the photographs are. That's not something you or anyone who'd purchase from you can afford to make a mistake on.
The second suggestion is make sure you have a good promotional/advertising campaign set up. Content is a highly competitive business and many a good potential content provider has been driven out of the business because no webmaster was familiar with the company or, in some cases, even knew it existed.
The Newbie Board will hopefully be helpful to you as freesite webmasters come here often. Also, don't forget the "non-sponsor forum" for direct advertising.
