Applying Alito's interpretation of the Fourth Amendment (and everyone who joined with him in the Jones concurrence), the fact that manned aircraft are probability expensive make them fundamentally different than a much cheaper technology. The idea is a reasonable person knows manned aircraft are super expensive and thus law enforcement will only use them in certain situations. Because of this, such activity is not considered a search under the Fourth Amendment. However, according to Alito, this does not mean that the search is still considered reasonable when the same activity becomes much cheaper. Indeed, he held that extremely lengthy tailing of a vehicle on public roads with a cheap GPS device constituted a search while the _same_ activity done manually by law enforcement did not constitute a search.
For what it's worth, I think the FBI's use of drones here is fine. I'm one of the last people on HN who would ever jump on this surveillance bandwagon/train wreck we are seeing. I bring this up because four Supreme Court justices believe that the cost of an activity can determine whether it constitutes a search (yes, it is not settled law). Because of this, drones being cheaper isn't actually an argument for them being ok. The correct argument here is that drones are cheaper, but still probability expensive to deploy en-mass against the public. If drones ever become cheap enough to do that (like the GPS device in Jones), then it's a whole different ballgame.