I've stayed a couple of times with a retired lady, Rosa Torrado, who owns a five bedroom apartment on Calle Arturo Soria in a very nice section of Madrid. She rents three of the bedrooms to students (which is how I met her originally). Also she is only one block away from a Metro Station on the #4 Line. Rosa charges 23 €uros per day which includes dinner every evening and coffee in the morning. She is a very sweet lady, but I should tell you that she does not speak any English. If you would feel comfortable communicating with her in Spanish, you can telephone her at (011)-34-91-300-0598. (She does not have email.) Feel free to let her know that I referred you to her. (She knows me as Arturo.)