@Aramar how trained is your staff? In the long run, it's much better to have fewer staff employees and have them all trained up to 5 stars than to have lots of them and none trained. If you have, for example, 3 habitats that are fairly close, and a keeper's hut/staff room somewhere near, then 1 fully trained keeper is able to handle all 3 habitats. The same goes for mechanics. Educators are also pretty expensive. I always put one educator down, train them fully and then have them in their own work zone, where I include all the animal talks that are somewhat near each other and then also put all the staff rooms in their work zone. So when they go from A to B to C to D they have staff rooms in between to rest.
I also suggest deleting the empty shops as they seem to lose a lot of money over time. Also, check the flow of your guests. They complain they are hungry/thirsty, but there are plenty of shops spread out. My bf had the same problem in one of his big zoos.
I would try raising the prices of everything as much as possible. Try breeding the exhibit animals and selling them to get a little bit of money. I would delete the monorail for the time being if it's losing you money.
Also, check your animals. Animals like lions can be quite expensive in terms of food. Try to enforce some population control, put animals on birth control to stop the breeding for a little while. Make sure you have enough donation bins. Also as Foxy mentioned, try increasing the radius of speakers as much as possible (as long as they don't overlap).
I don't know if you have tried any of this, but I hope it helps and you can save your zoo!