If you are talking about the panel itself, you would need to replace the whole assy.
Cost will vary from model to model (generation and screen size). Also, it depends on whether you want to buy new, or settle for used.
ifixit.com sells the 2011 13" panel for $599.00(used). Then you will need someone to install the panel, which could cost another $100-$200.
If you want new, I think someone mentioned that it would be in the vicinity of $750, parts only, from Apple.