I would recommend the following hotels if available:
Ibis Barata Salgueiro -
http://www.ibishotel.com/ibis/fichehotel/gb/ibi/3137/fiche_hotel.shtml
This is just of Avenida Liberdade and half way between the Baixa and Marques de Pombal.
You may find however from the time of year that hotels in the centre are difficult.
If so try the following which are in easy walking distance of the Praça de Espanha Metro Stop.
Ibis Malhoa
http://www.accorhotels.com/accorhotels/fichehotel/gb/ibi/1668/fiche_hotel.shtml
Novotel Malhoa
http://www.novotel.com/novotel/fichehotel/gb/nov/0784/fiche_hotel.shtml
(Check out cheap offers on the web)
I would suggest that you might want to take a two day trip at the beginning of you visit to either Coimbra or porto.
Both are easily accessible by train from Gare de Oriente 5 minutes by cab from Lisbon Airport. Porto is 3 hours by train from Lisbon and its river area is delightful. Coimbra is the home to one of the oldest Universities in Europe and although small full of Character.
