Flyaway, just to let you know, some CCCs do accept children slightly younger than 18 mths (subjected to MCYS's approval). My boy's previous CCC accepts children from 14 mths old if MCYS approves the case.
Some CCC have attached infant care & they give good discounts for siblings. Can start looking around.
If your mother in law continue to compare the $$$, then just shoot her that she did not give your husband a good education (PHD sort of thing if your husband does not have) so he only earns a limited amt, dont ask for more since she did not contribute to his success.