How much did it cost to build the concentration camps?

The cost of building a Labor Camp was Zero, Nada, Zilch. It was a profit making enterprise and here is how it worked: Joe gets a contract say to make widgets. He contracts with the SS for slave laborers who are skilled widget makers and pays the Nazi's a fixed price for each laborer for each day that he needs them. Joe's Widget Plant take the slaves and works them to death making widgets. He only feeds them enough to keep them productive and if they die, he contracts with the SS for more laborers. The profits made by the SS were enormous and more than adequate to cover the cost of establishing transit, holding and extermination camps. It was a win - win situation.