I remember it being under $1 at FP&L.
My aunt explained real shift differential: She gets 12% differential Friday, Saturday, and Sunday; 13% differential nights. You can combine them for 25% differential.
I know, you want to know what utility. Sadly, this is a hospital (and rather a common one at that). They know many people would rather not work nights and weekends; this lets those who REALLY want the money have it!
(Hold your breath for a nuclear plant to do it. But it would be nice!)