Massey, nearly impossible question to answer depending on what kind of finish out you're going to do. Are you going to have wood floors, carpet, granite, laminate, etc. A good range might be somewhere from $90 per square foot up to $200 per square foot, depending on the contractor and your finish out. I would get a few reputable contractors to give you some quotes based on the design you are thinking and go from there.
Joe Jarusinsky, Realtor/Master Instructor, Keller Williams Realty, Austin's #1 Real Estate Company, Ranked #1 by Buyers and Sellers (JD Power & Assoc. 2012) Call 512-261-4415