You'll find all hostels (called "hostales" in Spanish) with websites @ http://www.MadridMan.com/madridhostels.html . They all have their location noted below each link.

Here, I'll take a look for you....

Okay. Hostal Prim & Huespedes Amanda are the only two VERY close to the Plaza de la Cibeles. Others are much further away. And, of course, ALL are accessible by metro.

Best of luck! Saludos, MadridMan