The cost is going to vary depending on where you live. Its going to be much less expensive to hire someone in India than someone in New York City. Second, there is a certain amount of fixed cost involved. You will be charged more per sq ft if the total amount to do is small, in comparison to a large job. Third, is this a new installation? Were the walls built by a professional? And are they square? Fourth, are you a professional hiring out a subcontractor, or is this for a consumer? Lastly, from reading your post, you cannot write or speak english too well, so they'll probably charge you more.