Its probably out of the price range you are looking for, but the hotel Colone located on the Plaza of the Cathedrale is a great location and a pretty nice hotel. I think it may range in the 300 Euro/night. However, right behind it is the Grand Hotel Colone which I think is significantly cheaper. It is close to the ramba and walking distance from the Gaudi buildings and (possibly) Barcelonetta. The luxury hotels (no Four Seasons unfortunately) are all on the Diagonale.
Have fun in Barcelona, I'm jealous!!