I bought an order for $3.19 (and picked up an order of Chicken Fries as well for comparison's sake).
If you're wondering if you get more food with one or the other, both boxes had a very similar heft to them, which is to say, both were really light compared to say... anything else on the menu. The Chicken Fries Rings box is just slightly more squat and wider than the Chicken Fries box:
Nutritional Info - Burger King Chicken Fries Rings
Calories - 310 (from Fat - 160)
Fat - 18g (Saturated Fat - 3g)
Sodium - 1020mg
Carbs - 21g (Sugar - less than 1g)
Protein - 17g