I just purchased 30 sheets for my kitchen. I don't want to do it either.... I paid $8/sheet for it. Tomorrow at work, I can look up the estimated cost in RS Means Construction Cost Data. You'd then know if you're getting a good price or not. Getting drywall up to the attic can be a &^%^ too. Getting it delivered through a window for the installer might save you some money.
What's your zip code, or city/state?
How tall are your ceilings?
How many square feet of wall space? How many square feet of ceiling?