We were there over spring break and they had the Rapid Refill then too. Can't remember the exact prices, but I think they were the same as at WDW.
We actually do buy mugs at HHI but hardly ever at our resort in WDW. We find it is convenient and easy to refill at the beach house while we are at the beach. We love HHI's beach so we are there almost everyday for part of the day. Bringing mugs is easier than lugging a cooler down to the beach especially when we are already loaded down with chairs, umbrella, and sand toys etc..
Even at the main resort area the resort is so small, it is a short walk to refill. Our kids of course love to refill on their own too and its so small and closed in we feel very safe in doing so.