Here is a post of mine from earlier in the year where I broke down the actual costs of starting up a zoo. Note that these figures will vary considerably depending on where you build the zoo - the location given in this example will be on the very low end of possibilities.
Here's a real-world idea scheme. How many keepers do you want to have? You need at least two so that they can have days off. At a bare minimum, you'd better be paying them at least $25,000 a year just so they could survive. $30,000-$35,000 would be better. You're also going to need people to sell tickets and clean up. Here, you'd look at at least three people. You might (and this would be sub-minimum wage) be able to do that at $15,000 a year. So right there, in terms of 5 employees, you're already at a bare minimum of $95,000 a year. That's before exhibits, animals, food, construction, insurance, promotion/marketing, upkeep, supplies, utilities (gas, water, electricity), vehicles for transport. We could take a look at those individually too. Utilities, expect about $1,000 per month, so $12,000 a year (again, bare minimum). Insurance,: you'll need property insurance, liability insurance, health insurance for the workers, auto for your vehicles, plus a few other policies - here's look at a bare minimum of $50,000 per year (possibly higher for an upstart with no experience). Vehicles: you have to have something to transport the animals, food, workers, and supplies. A good truck will be about $25,000, add on to that perhaps $200 in gas every month (another $2,400 per year). In order to promote and market your zoo so that people actually visit, factor in $1,000 a month (another $12,000 a year).
So right there, we have $95,000 in staff salaries and $101,400 for services for a total of $196,400 per year (minus the $25,000 for the truck in years after year 1). This is before you have any animals, buildings, exhibits, or animal food. This also doesn't factor in basic supplies (tools, equipment, etc.), graphics, taxes, visitor amenities (like food, drinks, gifts, etc.).
Oh, you also have to buy the land. Let's say you want a 10-acre zoo. A small zoo in it's own right. I found a patch of 10 acres in South Carolina for $34,000. But, here's the catch, it's not easily accessible for the public. So, if you want something that the public can access via good roads and feel safe, I'd budget for at least double that amount - $68,000. Running tally is now $264,400. Oh, and you'll have to pay property and school taxes on that land. In SC, property rate is 4% up to 5 acres. We'll use that as a base rate (above 5 acres is determined by local jurisdictions). Four percent of $68,000 is $2,720, and that's just for the land itself. Once you've developed that, that number will go up quickly. That brings our running tally to $267,120.
Next thing you need to think about is sidewalks for the visitors. Say you have one mile of sidewalks - not unreasonable for a 10-acre zoo. The average rate on that is $204,000. You'll also need a parking lot. Be prepared to give up an acre of your land for that. Going rate for an asphalt parking lot is roughly a dollar a square foot. At one acre, you need to budget about $40,000. Running tally - $471,160.
Note: we haven't built anything other than the sidewalk and the parking lot so far. There are no buildings, there are no exhibits, there are no animals.