To start something like the Granby Zoo from scratch would be terribly expensive but you don't have to do that. Like
Architype says, you could start small and work up.
The Magnetic Hill Zoo began as a provincial wildlife park, but the city took over, added a petting zoo and began bringing in exotics. The zoo was pretty shabby when I moved to Moncton in 1989, but the city hired a professional zoo director at about that time and adopted a program of upgrading one exhibit per year (at a cost of perhaps $100k) so that today, the zoo is something to be proud of.
Exotics aren't necessarily all expensive. Large animals requiring big exhibits and special care (elephants & giraffes) can be. Pandas are
ridiculously expensive so I can see why Granby bowed out. Primates and large cats on the other hand are fairly cheap, so mid sized zoos like Magnetic Hill tend to concentrate on them.
Our zoo benefits from municipal support and subsidies. In addition, the "Friends of the Zoo" do a lot of fundraising and other monies are raised through the zoo gift shop and admission fees. The zoo is also strategically located at Magnetic Hill next to the Magic Mountain Water Park, so it is in a popular tourist area. I think the zoo may get 150,000 visitors per year. The zoo has built support in the community by having educational programs in the summertime (things like zoo camps where kids of different ages are able to shadow the zookeepers while they work) and by having special events like "Boo at the Zoo" at Hallowe'en where the zoo is decked out in spooky exhibits. This event is so popular that tickets are sold out well in advance. The whole zoo is very professionally run and future plans
may include additional exotics, even giraffes. I know that they want to expand the African exhibit area even more than it already is.
My advice would be to start small (like a petting zoo) and add exhibits gradually (perhaps starting with crowd favourites like big cats and monkeys), build support in the community and have "events" in the grounds. If you concentrate on adding one quality exhibit per year, within 10-15 years you will have something to be proud of.