Hello.

Although very late... it`s better then never!

Ok, there are many places to live in Lisbon with that configuration.
You may find some advertises in here:

Find the ocasião site in google / Imocasião and then:

Mercado Imobiliário - Arrendamento (renting).
Txx (it`s the number of bedrooms the flat has. xx= 0 the flat is a big room, with kitchnet bla, bla).

Places to look for:

Alfama/Bairro Alto (old part of the city) - center
Saldanha - center
Campolide - outside (good public transports)
Benfica - outside (good public transports)

Then you can try Expo-area (Parque das Nações) although not cheap!

Then you can live near the sea along the cost.
You can find cheap apartments in Paço D`arcos/Algés/Oeiras - 15 minutes by train and you are in the center

Hope you enjoy your stay