I have seem them for 3 for $5 at the grocery store, which is still too much in my opinion. Im sure in bulk they can be bought for cheaper somewhere. I know at costco they ahve them at a case of 24 for around $38, also at local Korean stores here for same price. That however is not sugar-free Red Bull, only the original.
Here in Austria, we recently got Coke Light Lemon ("Light" is used in German for "diet"). Not all that bad. I really can't drink the stuff without lemon or lime. I wish we had the huge selection of diet drinks available in the U.S.