While not certain, I seriously doubt there are ANY "hostales" near the southern Madrid Méndez Alvaro bus station (called "Estación Sur de Autobuses) & metro station of the same name because this is not a tourist zone. I doubt there are any hotels either but there may be a smaller one within a few blocks.

I can tell you with all certainty that there are no "hostales" with a website near the station. Still, there may be one within a few blocks which does not have a website and is largely unknown to man.

Sorry! Still, it's probably only a 15-20 minute metro trip from one of the more close-to-city-center stations where there are more "hostales" from which to choose.

Good luck!

Saludos, MadridMan