I personally recommend staying in Viñales and visiting the attractions in Pinar del Río on a day trip.
There is a host of casas particulares in Pinar del Río. Most charge between CUC$15 and CUC$25 per person and usually offer reasonably priced meal options. The Casa de Tebelio and Mayra, Calle Colón between Mariana Grajales and Juan Gualberto Gómez, 50m (164 ft.) from the bus station (tel. 48/77-8050), is a nice casa that offers one room for rent, an attractive garden, and two terraces.