Does it need to be sweet? I love all the True Lemon drinks - the originals (lemon,lime,orange,grapefruit) are just dehydrated juice. 1 packet is like a wedge. I think I've seen them in Publix when I've been near Tampa.
They also make sweetened drink mixes, but they are not calorie free.
Lost the first 100 with Medifast, now working on the last 25