I tried this out of curiosity and, yes, when "Whole Word" option is on you will not find the suggested text.
I can only surmise this is because '$zone' is not considered a 'word'. If you substitute the $ for any other symbol the same result is given.
Clearly then the title of this thread is incorrect, 'find text DOES work', when you understand the the constraints of the find options.
In your example there is no practical reason why you would need to use "Whole Word" to search for instances of '$zone', just do a 'regular' search.