The south is a big area, you need to specify where. I know mostly about Mogadishu.
Land in Mogadishu really depends where you looking at, if your looking at any of the inner suburbs like Wardigley aka Warta Nabada or Howlwadag where Barakaha is located, its quite expensive from $90k to 250k inside Bakaarah markets. However the most expensive by far is around the KM4 area, where some of the prices are mind boggling for Somali standards, I heard up to a million.
The good thing is that you can get some really cheap land too, I think around the outskirts of Medina and Daynile its around 15k to get a piece of land. Furthermore, new estates are popping up such as Darrusalam city with the median price between 70k to 150k.
Other then some areas in Mogadishu, I doubt land is expensive in the South