Unmanned robotic spaceflight is pretty cheap in comparison to manned. Cost of throwing up a satellite averages about US$50 million now days, compared to $500 million for a shuttle launch. Heavy lifters to get mining equipment to orbit might be more like $100 million. Upper stage booster to take it from orbit to the asteroid plus return mined materials would add another couple hundred million. The robotic mining equipment probably isn't very expensive. I would guess total cost to send up a single mining robot and return a batch to earth is probably around $500 million.
Must be some good stuff on those asteriods to make it worth the effort.
Must be some good stuff on those asteriods to make it worth the effort.