Last November, I stayed with a retired Spanish lady living alone in Madrid in a five-bedroom condo (some with private bath) in a very nice part of the city. This was arranged for me by the school where I was attending Spanish classes. (The lady does not speak English.) The cost was very reasonable and the lady very nice. She's always interested in renting out some of her bedroom space to visiting students. If this appeals to you, send me a private email and I can provide you with her address and telephone number.