Maybe you're a more tolerant peregrino than I am, but I personally would not want to go to any of the youth hostels in Lisbon. There are some that are very nice, but I think the college party crowd's interests are likely to be different from peregrinos' interests. If you want shared bunks in a dorm room, I think the best bet is the albergue juvenil that rooky recommends, the Pousada de Juventude in Moscavide near Parque Nacoes. That one is far enough away from the center that it probably won't have the standard college crowds.
But if you want something like a pensión (called pensao or residencial in Portuguese), I would recommend looking at the following places. I haven't stayed in any of them but I scrolled through the low price options in Lisbon looking for things that were not youth hostels but had private rooms, none more than 25 €. All are well reviewed on booking.com
http://pensaoduque.wix.com/henry Near the ferry terminal, well connected, not the most atmospheric part of Lisbon
http://www.pensaoprata.net/v1/ Extremely central, well rated, in the Baixa area close to subway and the hearts of old Lisbon
http://pensao-elegante.lisbon-hotel.net/en/ good location but a little further from the core of the oldest parts of Lisbon