The SEC's much ballyhooed conflict minerals disclosure rules reportedly have done nothing to reduce violence in Congo and in some ways has made it worse:
GAO found no empirical evidence that the rule has decreased the occurrence or level of violence in the eastern DRC, where many mines and armed groups are located. GAO also found the rule was associated with a spread of violence, particularly around informal, small-scale gold mining sites. This may be partly because armed groups have increasingly fought for control of gold mines since gold is more portable and less traceable than the other three minerals. Further, GAO found that the number of violent events in the adjoining countries did not change in response to the SEC rule.
Reliable data on costs is hard to come by, but is surely in the hundreds of millions of dollars over the years.