Zoos in city centres or suburbs are always likely to charge high costs for parking, not least because their car park would be overtaken by non-visitors very quickly if it were found out to be free or cheap. In addition, as others have suggested, those zoos are much more likely to be accessible by public transport, which should be encouraged - and the cost of land is higher in those locations.
Out in the sticks there's much less justification - public transport is often thin on the ground (wrongly, of course, but we have to deal with reality as we find it!) and there is likely to be little other reason for anyone to want to park there.
I do remember being rather taken aback by the charges to park at Selwo Aventura - it was about €10 as I recall to park - right at the furthest edge of a loose urban area and a fair way from a bus route (and entrance wasn't the cheapest already!).
Out in the sticks there's much less justification - public transport is often thin on the ground (wrongly, of course, but we have to deal with reality as we find it!) and there is likely to be little other reason for anyone to want to park there.
I do remember being rather taken aback by the charges to park at Selwo Aventura - it was about €10 as I recall to park - right at the furthest edge of a loose urban area and a fair way from a bus route (and entrance wasn't the cheapest already!).