There are only 2 ways unmanned aircraft save money... reducing the size & complexity of an aircraft by removing the cockpit & life support systems (including bang seats), and reducing the training costs for aircrew (note I said reduce, not eliminate).
The main drive for unmanned aircraft comes from 2 points... eliminating the political cost of losing pilots in combat (or having them be captured), and increasing range and/or payload due to not having to consider human factors in aircraft design and mission planning.
Even so-called "autonomous" combat aircraft still have data-links allowing a controller to monitor it in real-time, and to take control if the situation changes or something malfunctions... and this communication is subject to jamming, etc, while a piloted aircraft is not.
In a manned aircraft, the pilot is "on location" and can make changes and decisions without communicating outside the aircraft.