Ehh... Watch it. In MA it can't be classified as a flash-hider. So you need to MAKE SURE it is a muzzle brake.
If you need threads cut, I believe it will be over 100 bucks as that is a big job. Out of curiosity, how long is the barrel? If it is over 16 inches you could probably find a muzzle brake that attatches with set screws as it wouldn't need to be pinned (over legal length, and no exposed threads).
Mike