The main bus station is at Sete Rios metro stop, which is also where the Lisbon zoo is. There are several moderate chain hotels in walking distance, on Av. Jose Malhoa. These hotels were all built for the Lisbon Expo (92?) and there is an Ibis, novotel, mercure and several more. But I have to say it is a totally charm-less part of a city with a lot of charm in the historic center. The metro is very efficient, and If you want recommendations on places that are more central, close to a metro for getting quickly to Sete Ríos, happy to offer suggestions (for low cost budget pensión type place I always suggest Pensao da Prata).
You may have your reasons for taking the bus, but I have taken the train and it is quick, efficient, and you can get it from the downtown station, Santa Apolonia. Bom caminho!