Right you are Greg. Helicopters are not cheap. This I know for a fact. This is also probably why they are not used very often for railfaning adventures, along with the fact that the guy gets lynched by the poor, ground bound, railfans with video cameras as soon as he lands.
Of course, like you say, you could always us that "whisper mode". Too bad they only exist in Hollywood. I guess you could dub in some proper sound in the editing room but like you also said, you are going to start to need a budget that also only exists in Hollywood.
Maybe you were right about the "tracks to Gato" first.