Hotel Sidi Bou Fares
15 rue sidi bou fares. right in the centre of town. all rooms are based around a pretty central courtyard. they are rather small, but are en-suite. single room rate oct '07 was 45 tnd, but it can be haggled lower.
There are a couple of places to stay in Sidi Bou Said itself.
You can easily find hotel rooms in nearby Tunis or Carthage. Additionally, if really lucky, you might rent a room for a night or two in a house, from a village resident. However, this is rare, since the locals are quite rich and rarely have any interest in sharing their home with total strangers.