I used to stay at Casona Dorada a lot. They are between 35-50 per night. The rooms can be inconsitent, so ask to see a few and pick one. They have a restaurant, small pool and a disco/bar.
They are right on avenida independencia in gazcue, so you can walk to the zona colinial as well as to the big casinos such as the Juragua etc.
It is also a short walk to the Malecon. Location wise in that price range, I always stayed there.