Marriott does not guarantee cribs:
https://help.marriott.com/s/article/Article-22515

Thus, OP had a request not a reservation for a crib. That likely explains why the manager would not cover the purchase price and why anything Marriott does is a simple gesture. I would not expect the stay to be comped.

Where something matters, I would have a conversation with a specific person at the property and assure that there really is a crib or whatever item it is and ask the individual if they could set it aside somewhere or do something to improve the chances that it dosn't go wandering.

The question of who sleeps where is a personal one and should not be part of the debate about the reservation.