While you can pay more for a hotel room in Milan than you would almost anywhere else in Europe, there are also some decent accommodations at reasonable prices in good locations. It's difficult to find rooms in any price category when fashion shows and trade fairs are in full swing (often in Oct and Mar). Many hotels raise their prices at these times, too. August is low season, and hotels are often willing to bring prices down considerably, as they will sometimes on slow weekends. Rule of thumb: Always ask for the lowest possible rate when booking and be prepared to bargain.
Inveterate shoppers will want to stay in the Brera/Magenta neighborhood, avid sightseers near the Duomo; budgeters will find the most options near the central train station and along Corso Buenos Aires.