Simplest solution is not to pay the ransom, which is a lot easier when it's a drone than a ship with crew. That eliminates the possibility that actually hunting for them becomes a viable business model unless you've got a high-value black market for any of the on-board tech, and I doubt they'll send many near the coast of Somalia or Mindanao where there's a relatively high density of pirates that might steal them out of sheer opportunism.