I don't work in the feild but my girlfriend works at a zoo and 80 grand is more than double what she makes. I also have several friends that work at the San Deigo zoo and they don't make that much unless they are a head keeper or a vet. It is a lower paid feild for a basic keeper because it is a job done out of passion for animals so if you don't want to work that cheap they just find another person. As far as opening a zoo or a pet shop there is nothing that says you have to have a degree. As far as opening a zoo it is very expensive the zoo my girl freind works at started as a bird farm and just eventually grew into a zoo.
That is my two cents