you could try selling things that you dont need, make paths smaller, if you use pits, you can bulldoze some of the fences, try putting paths 1 square away and only a couple up next to the exhibit, and only put fences where the path is. it probably wont make a whole lot of difference, and i have money problems too. i just build it up real slowly and try not to spend too much on my guests. you could also use cheaper animal food
example: some animals will eat hay or grass. instead of placing hay, place grass. also just use regular piles (not food dishes/troughs, they are more expensive) and dont place water dishes/troughs, just put a small circle of shallow water from the biome they live in. even if they dont swim, they dont usually get stuck
p.s. you probably had so much money in the second-generation zoo because you didnt have to adopt animals