disparity

“The disparity in standards of living between rich and poor is always high.”
Is this sentence OK?

I wouldn’t use ‘high’ there because you are looking at a difference between two things. As ‘disparity’ already indicates a great difference, I’d word it in one of these ways:

The difference in standards of living between rich and poor is always great/large/wide.
There is a (great) disparity in standards of living between rich and poor.