You asked this question at just the right time
JUST yesterday I THOUGHT I seen the price drop on our next cruise by over $200! I submitted the claim form (Linked in another post above) but shortly after realized that we had added the $109 price protection (X 2 guests = $218) to our cruise and this difference ended up being the price difference for what I was looking at
BUT Carnival did reply with a link that makes it MUCH easier to check the current rate on your booked cruise! See below, all you need to know is the category of your room.