I've noticed that carnivore food costs are 8 to 10 times higher than that of herbivores. Not too long ago I started a zoo with Komodo Dragons and was barely able to turn a profit for the longest time. Normally I didn't have this problem as I started my zoos with a tortoise enclosure but I wanted to mix it up a bit. I don't think this is a bug, it's by design. You can check the animal's feeding costs on the habitat menu when you select the habitat. It would be nice if projected food costs would be listed somewhere before I adopt the animals.
I have the same animals in my secondary zoo since almost 40 ingame years.
It has only 6 habitats.
One year i have food expenses of 70.000 $, the next year of 95.000 $
Then it can go back to 80, 90, 65, 110 from year to year.
I checked a habitat with 5 gorillas, it caused 8,503 $ last year accoring to the game.
Another habitat with 6 gorialls caused 20.000 $ (exactly the same layout, size and food enrichment).
Now i have a crocodile habitat that went out of hand (my fault) with 12 ! crocodiles.
That caused 8.501 $ in the same year.
Both are at Food Grade 1 (and i shouldn't have to give my furry friends food to be able to afford them)
It is complete arbitrary.