You'll find a few northern hostels on the Madrid Hostels page @ http://www.madridman.com/madridhostels.html , including a couple at Cuatro Caminos, Tribunal, Glorieta de Bilbao among them but these are all still a long walk from Moncloa. Luckily, all these areas have metro stations and you may also be able to take a local bus from one to the other. Good luck!

Saludos, MadridMan