Been to Istanbul once. One of most beautiful cities set on hills along Bosphorus. Hotels seem expensive due to weak Pakistani currency. Food is cheaper especially Doner Kebabs, etc (very very tasty) around Istiklal square and Sultanahmet.
I recommend staying in various hostels. See this amazing site. I always use it. Hostels in Europe, Backpacking Europe, Backpacker youth hostels in Rome, London, Paris, Europe
Also see Travel Guides, Hotel Reviews, Photos, Forums, Deals - VirtualTourist.com and TravelBlog | Travel Blogs, Journals, Diaries and Photos
All the best!