They were about $12 last year. They can hold hot beverages, I think coffee and hot tea are available at some refill locations (nonthing fancy like latte's though). Fountain soda may be available at additional refill locations (i.e some pool bars)
You can only refill in your resort (not the parks) and the location is usually the CS location (somewhat inconvienent to get to on a regular basis)
With in-room coffee makers and fridges it is much cheaper and easier (do not have to get dressed up when you go to your fridge) to bring your own beverages into your
DVC room...