If you break it down, there's the time it takes to remove it, strip it, transport it, set-up time at the machine shop then machining time, any machining work would have to be inspected and passed, transport back to the tuner, reassembly and fitting.
Everyone takes a bite of the cherry and there's still a profit to be made. As long as there's people who don't have access to machining facilites and the expertise to carry out these mods there will always be tuning companies that will gladly take your money.
dunno..