Here is the exact line from a translation that I am reading:
I just read it as あずけがね and continued on. Then, I decided to double check the meaning in my dictionary. But it had it read as あずけきん. And that reading seemed strange.
So, this is a professional translation. So, I am pretty sure that:
(1) あずけがね is the proper reading for this context.
(2) あずけがね does not sound slang.
(3) あずけきん is a proper noun that is almost exclusively used with regard to apartment rentals?