Peter T. Daniels wrote:

So it's your recommendation that our 5- or 6-day visitors spend
several hours in Downtown Brooklyn first? Just _finding_ the MTA
building is a challenge.

Normally you'd be correct. However these visitors seem especially keen
on minimizing expenses, though perhaps not because they don't realize
how quickly the transit expenses in and out of Manhattan will add up.
Clearly a better use of time would be in finding a less expensive hotel
in Manhattan than trying to figure out ways of saving a relatively small
amount of money on transit.

I'd recommend a visit to Brooklyn to visit the NYC Transit Museum.