This backpacker hostel is a bit pricey for this bracket, but the staff is helpful, the rooms are heated, and you can have your own bathroom. Added bonuses include a book exchange, hot showers, public kitchen, and a communal lounge where TV and Wi-Fi are available. A bunk in a dorm room will run you (Bs)53, compared to (Bs)150 for a private room for two. The hostel is also very central.
Junin 56, Potosí, Bolivia