I assume that you are asking about labor costs, since you must have the materials already.
For hanging and taping (floating/coating) and you do the sanding (it eliminates the cost of the contractor returning a second day) = I'd say, ballpark $400 to $600. Of course, that is in my region. You "may" find a price for less in your region.
Sure you can find a bozo that may have a cheaper price, but cheap and quality don't equate.