If you look at the cut open V2 rocket in the Imperial War museum in London you can see about 1/3 of the innards is the control system; gyro's, inertial guidance etc. Today you can buy that on a chips from digi-key, farnell, sparkfun or wherever for say $50 or even just root your smartphone and use it as the control system. It always surprises me that there is very little precision rocketry or ROV proliferation amongst the countries and political/religious movements with extreme agendas out there.