If you look for accommodation, preferable areas are: Bica, Chiado, Principe Real, Baixa, Bairro Alto – all at walking distance from the conference venues. Here are few suggestions, including hotels and apartments.
A few hotels:
1 bedroom/ 2p, 40€ night if you contact directly: firstname.lastname@example.org
see photo here: https://www.airbnb.pt/rooms/1322354
2 bedrooms + living room, from 67€/ night
1 bedroom + living room, 2 persons, from 53€/ night