Sheetrock and drywall are normally interchangeable...but before the rock goes up all of the framing wiring / plumbing etc. needs to be complete. has all of that been done?
"ballpark" rates for just hanging and muding sheetrock is about 1 to 1.50 a sq foot...depending on the job size...this may go up or down...generally the cost for small jobs is higher and once you get going there is some economy of scale.
Best thing to do....find 3 local contractors in your market and get pricing. Homeowners often think that they can handle the finishing themselves....that's really the hard work and best left to professionals if you want it done right.
Thanks I call few different contractors and made appointment with them so I will see what they will suges me.