There's like a tonne of factors that can determin how much you charge, or are charged for work.
Prices will always vary based on how much the artist feels thier work is worth, and if they want to go with the unwritten charging limits or not.
Generally you'll find most freelance artists will try to provide a service that caters to each person who would want to commission work. You'll often find if you contract for a bulk set of work, say 20 models rather than contract 20 individual pieces of work.. you will be charged by the hour/day or just be given a discount.
Model / Texture Packages are always a damn sight cheaper than freelance, but you don't have the personalisation. Always be sure to check on a Freelancer prior to contracting them. If there is no work available, then hold off until you can see something. Try to find out how long roughly it takes them becuase no matter how good the quality is, if they're charging per hour and take a week on just a character that is going to be expensive as hell.