Strolling 10-15 mins.
In Le Gourmet, a Russian owned Tunisian restaurant the wife and I paid 21.50TD for a 3 course set menu, 1.5 litre bottle of water and a basket of bread. That was in May 2009.
The restaurants opposite the medina are slightly more expensive than those on the back streets. In Tunis we ate (1 course, big plate though) for 7.7TD for both of us, again with water and bread. Today's rate 1TD = 46p.
At first 2.5TD for a starter and 7.5TD for a main, seems cheap enough, but once you become Tunisian-ised you'll be looking for starters at 1.5TD and mains at 4.5TD.
You really can eat good Tunisian food for around 8TD (less than £4) per person for a complete meal, with water and bread.

I'm certainly trying that one in September Kevin. I'm in Denmark at present but couldn't resist checking in here.

Hi Aslemma
Hope the weather is being good to you there, in Swanage it is lovely at the mo'.
This is the only restaurant that I've eaten in and enjoyed the "Tunisian" feel about the place in Sousse, the year before we had a terrible meal in one of the restaurants attached to a hotel on the front, it appeared to be closed this year.
The other time we ate in a tourist resort we were in PEK and the prices were all higher and the food had a very "English" Tunisian taste about it. As you know we eat a lot of traditional home cooked Tunisian food when we are there and this restaurant's food had that same taste about it.