The batcave, in any version of Batman, is large. Plus there's the batmobile, which required special construction, plus the batcomputer and numerous other batwidgets.
How did a good sized batcave get built without the land above it being torn up and without requiring a huge construction crew?
And, after the cave was built, how was the batmobile built in secret, without someone involved in it being able to make the connection between the car they built and the one that shows up in the news when Batman is first seen? (While he's in Gotham, a masked vigilante is news that would end up nation wide.) There would also be the need for secrecy so vilains can't find out how it is built and what the specs are.
And then there's the continual supply of batwidgets. Just as with the batmobile, there's the need for these items and how they work to be kept secret.
It'd take several factories to produce all that Batman uses and major construction for any batcave I've seen (which is in movies and on TV).
How is all this done in secret? (Or is there a trail of bodies?)