there are quite a few web sites out their helping with pricing guide lines.... heres one of the ones i first used ...
photography tips | How Much Should You Charge for a Photo Shoot

another one here
Stock Photo Price Calculator
the main thing to remember is not to under value your services! if you do not value yourself no one else will!

when choosing agencies to sell your work... check their prices as a buyer first before yo sell through them! micro stock sites devalue the amount off time and effort you have put into each image.

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