Typically you have a choice 3 thickness types. 1/2 inch 5/8 inch then you have your water resistant drywall. Use the link to study and figure out what type of drywall you need and then get local bids from local pros. Thats probably the best way to figure out pricing. I think each area will be different. Getting 3 to 4 bids and knowing what type of sheet rock you need will help you get the best pricing. Also if yo have an older built home it might be using gupsum board - which is a little different. If youre not sure get a pro to take a look to be sure you're ordering the right stuff. For new construction, just be sure you have the right size.
Without knowing all these, one can't answer your question perfectly. You should visit an expert or find some quotes from websites. To find the websites, simply search them on Google. If you want a little help from me, I may recommend you to pay a visit to: http://www.getproquotes.com I read their article a few days ago and recommended them to a friend. The friend was happy to deal with them. The article is here: http://www.getproquotes.com/prices-and-costs/drywall-costs.php