i think its cheaper because mechanics and pilots have to constantly check if the EXTREMELY complex autoland system works, if it fails during low visibility - a diversion is needed, while in a HUD I'm quite sure that the system is much simpler since all it requires is to display primary display in another place (ie the HUD). I also don't think that the HUD system is new since a lot of old fighter jets already had that system and pilots coming from the military (back in those days) could have already known how to operate so the retraining would have been much cheaper for the operator, thus saving money once again.