The cost of robot is high, because a robot includes mechaniques, electroniques, computer technique and intelligent controls. A robot must be packaged with all these techniques. As we solve the whole problems of robotics, we need height of experiments, control theories, strong and robust mechanical structures, and a good electronic designs. And the brain of a robot is your algorithms. They are packaged. A package of 4 difficult fields need to be paid back with high cost.
I didn't work on bomb finders, but basically, a bomb finder must be a mobile robot, equiped with a bomb finder sensor which may metal detector or something like that. Some types of bomb cannot be detected with metal detector for example magnetic bombs which was dropped on over of Vietnam years ago.
Everything you need to build a bomb finder that you have to determine which type of bomb need to be found and you use the suitable sensors. After that, you build a mobile robot which may move upon a 3D land at low speed. The problem here only come from bomb detector (sensor). I've never worked on this field, therefore I don't know muchie bout this. But you may search for sometypes of them from internet and nasa pages.