The price of the cups are about $8, and no, you can't use it as a snack option. A frozen drink itself ($3.25ish) or a refill of said reusable mug ($3.00) is an allowable snack. I don't have my pix uploaded yet, but there are Goofy, Minnie, Stitch and non-specific princess bases & toppers for the mugs, and the colors of the mugs themselves are green, blue, red & pink, as I recall.
As for the drinks themselves, there are several flavors. There is a frozen Coke, cherry, apple, grape, orange, berry, and might be one or two others. I've had enough frozen Cokes to know I like them, so I skipped that at Goofy's so far. The apple is kind of unique...like a slushy version of apple juice. The grape is like grape Kool-Aid, but a more concentrated grape flavor. Orange is similar to an orange dreamsicle. At this point, I haven't tried the cherry or berry, but would assume they're just like an average slushy of that flavor you'd find elsewhere.