Hey guys after dealing with this myself, and reading the posts in this thread I think I've kindof figured out the issue. It could be a bug, or working as intended depending on the POV, but I personally believe it's a bit of both. Which could be why it's so difficult to track down.
I think the problem comes with growing our franchise zoos too fast, or another way to put it, is growing them too fast for the mechanics of the game.
PS TLDR at the bottom for those that don't want to read my novel.
The problem comes from bringing in too many of the big ticket species before your zoo and guests are ready for it. I know in my experience I had a couple different exhibits with african and american herbivores and combined a hundred or so animals, and when babies were born I'd move them to another exhibit to grow them out and when they grew up I'd sell them for CC and strategically replace the parents (females with my babies, and new fresh males from the market) to keep the genetics pure and produce better animals. Basically I was farming them, (whatever you think about the ethics of this has nothing to do with it, I wanted CC to get big ticket animals in other zoos) it was working fine with herbivores and I had a 200,000+ CC. I wasn't making a lot of money but I wasn't losing any either.
Then I thought Lions go for big CC and they can survive with 49 females and one male. I thought I can bank off of this! That is when it all went to crud! One problem is herbivores = cheap food and carnivores = expensive food. The other problem is I didn't have the donations from my zoo to support a large amount of Lions. By the time I got 20ish adult lions in my zoo and about 20 babies in a sister exhibit, it was too late, I had 30k in donations a year and 85k+ in food costs one year up to 120k in food costs. In another zoo I saw the same thing when I tried to farm the grizzly bears for the franchise community goal. When I got significant numbers of adult and baby bears my budget tanked before I could get the babies grown out.
Additionally when I started to get rid of the lions in the first zoo to find the problem when I got them back down to 3-4 lions the budget stabilized but the damage was done as I was 1mil in the hole. I could have eventually bailed myself out by farming and selling animals for cash but it was easier to start over.
This could be by design to keep us from "farming" animals for CC. But I think there is a bug in the way the food is calculated. As stated numerous times in earlier posts that the cost is per kg of food and not per feeding as noted in the UI. Maybe the balance here was calculated based on feeding numbers but when you get to feeding significant amounts of kg of high cost food, it skyrockets. If you only keep a pair of Tigers or a Pair of Bears or a couple apes, you might not see the problem or even notice. By the time you get rid of the babies a couple years later your budget can absorb the additional costs and your fine. But when you try to keep significant numbers of big ticket animals that eat lots of food the balance issues show itself and we have these issues. If you look at the screenshots above you can see they the issues are higher numbers 5+ of big ticket animals.
If you don't get big numbers of the big ticket animals (I'm looking at you Lions, Tigers, Bears, Big Apes, Elephants, etc.) but when you do, the balance is off, at least in my opinion. You could fix this by making the cost per kg of these foods cheaper for the big ticket animals and this could alleviate this issue. However maybe this is by design as feeding 40 lions, or 20 elephants, or 10 Orangutans, is going to be insanely expensive. And a smaller zoo just can't handle it. Maybe we should start with lower numbers of herbivores then grow that to larger numbers that can support the big ticket animals. Maybe farms are bad. I dunno.
If the price of feeding is truly per kg the cost per kg of feed should be the same for Elephants and Springbok, it's just hay and grain after all. The difference is the amounts you feed. Does anyone know if the price per feeding in the exhibits for these two animals are the same or different? If it's the same, and we do really pay per kg and not per feeding, then there is your problem. Change the UI to say per kg and make them the same and just feed the elephants more. There is your bug.
Anyways just my two cents, but there you go.
TLDR: When you get large numbers of carnivores/apes/elephants the costs get so high that smaller zoos can't keep up and costs get run into the ground. Large amounts of food is needed for larger animals and when it is priced by kg instead of by feeding adds up big time. Maybe we can adjust the per kg cost of food for larger animals or maybe it's by design. Maybe feeding 20 elephants or 40 lions shouldn't be cheap. However there could be a bug if we are priced per kg and not per feeding. Price per kg for Elephants and Springbok should be the same (grain and hay), but the quantities should be vastly different. This is where the bug could be, if it was balanced on price per feeding but it's really price per kg, an adjustment needs to be made.