Tunis to Douz is about 426 km in a straight line and around six hours by road — so the Sahara is not a day trip from Tunis, whatever a listing may imply. Two days is the realistic minimum, three if you want the Star Wars sets or the mountain oases as well. Tozeur, the other desert gateway, is about 371 km.
Not sensibly. The round trip is over 800 km of driving, which leaves almost no time in the desert. Every honest itinerary from Tunis is two days or more.
Around six hours, depending on stops. Most circuits break the journey at El Jem or Kairouan rather than driving it straight through.
It can be, if you only want the oases and have little time. But there are no transfer fares published for Tozeur airport here, and a private circuit by road lets you stop at El Jem, Kairouan and the Chott on the way.
Distances are straight-line, measured between the coordinates on our map of the sites; road distances are longer. Prices are per vehicle and come from the same database the 28 tours and 1,392 transfer fares are quoted from.