Star Hotel & Guest House
This clean and simple hotel offers a variety of accommodations suitable for all budgets - from double rooms with a private bathroom and television to dorms at very affordable prices. Rates may vary from 10 to 30 euros and with breakfast included. Its proximity to the major sights of Sultanahmet (only a hundred meters from the Santa Sophia, for example), the friendliness and availability of its owners, and the fantastic views from its terrace are some of the points that work in its favor.
A tip: If you go to Istanbul without a reservation during the high season, it is very unlikely that you would find accommodation throughout the city. As a last resort you could ask the hotel if they would allow you to stay inside this fantastic terrace that has the best possible views of the city even while you are going to sleep. That's right! Surely the recitation of five o'clock prayer in the two adjoining mosques will awaken you. (I recommend using earplugs to sleep.)
It all depends on what kind of night you are looking for; I slept on the deck under the stars and I can say it was an experience I will never forget.