This is one of those "How long is a string?" questions. There are too many variables to be able to even give you a WAG. Labor costs vary significantly from area to area. Even if you had a general idea of the cost per square foot of installation for new construction in your area, drywall installation will be considerably more in old work such as finishing a basement. Your best bet is to contace two or three drywall installation firms in your area and get estimates.