It is VERY hard to answer that question, because there are so many variables. Trex or wood, vinyl or iron handrails, through roof access or outside stairs, on and on.
By and large, people downtown are spending anywhere from $4,000.00 to potentially $15,000.00 on these decks and even MORE if you really want to put some bells and whistles on it. Its all in the finishes.
I would be glad to help with the entire project, from estimating, project management, helping you find and get a contractor under a legal contract, of course the Renovation Financing and even stay with you until the project is finished.
Please contact me if I could be of any assistance. :)