Spotlessly clean if rather austere hotel near the main entrance to the medina. small singles from tnd 13.
Midrange
$$
Abou-Nawas Boujaafar
4-stars. great food and services. thalasso center with an interior 30'c, salt water pool, another outside and private beach. 3 restaurants. deco from the 80's but not expensive. 5 minutes away from the medina and near all transportations.
Don't compare the category directly to european hotels. Expect to take a star or even two from these hotels. 4/5 star hotels are recommended.
Budget
$
Hôtel Gabes
12 rue de paris, in the medina. tnd 7.5 for a spartan single room; but good location and trustworthy staff.