Just a few notes about the Hostal Barrera , which is at Calle Atocha, close to Metro "Anton Martín" and (like most of those Hostals) close to the center, too (15 min. walk).
For the first two nights we had a quite small and somehow noisy room close to the receiption desk. But then they moved us to a very (!) nice room in the rear of the hostal where we stayed another five days. Both rooms have a modern and tasteful interior, TV, bathroom, everything looks quite new and clean.
The people of the hostal are nice and helpful - unfortunately we only learned on the very last day that at least the younger lady speaks some English, too.
Fazit - for only 50 Euro for a double, this place is a recommendation. Just ask for the "King Size Bed"... And try the bars in that area, too (C. Huertas)!

P.S. We had to give our credit card details to book the room by e-mail, which was kind of weired for the preparation of this trip. But this seems to become a habit because of "fake bookings" (see another spread in this forum).