There are so many factors..but I would estimate that it would cost you between $50 and $70 a square foot..but there are so many variables...including which contractor you hire the only way to get true estimate is have a contractor visit your site.
There is a also a website that gives cost estimates..for remodeling www.remodelormove.com
. Its free and easy to use.
As far as finding a contractor - I suggest you spend a lot of time looking and interviewing. If you can have 10 visit your home and give you a quote the chances of you finding a great one at a great price are pretty good.