Over here, at your neighbor to the east, it IS rather expensive if you visit just once.

But most locations offer a ticket for a year, sometimes even for a family for a year, and become very affordable all of a sudden if you visit four to rive times a year or more.

Since most of the zoos over here also offer mundane attractions for kids (fancy playgrounds, petting zoos and whatnot) it's a decent deal and in my experience something that works quite well.