I too am concerned about the amount of sugar, so I only use 1-2 oz apple juice and then add water from there. It doesn't bother me one bit, though I am pretty far along in my yeast recovery.
Martinelli's will be easy to find, though I prefer natural organic products or even juicing it myself. It has only 2% daily Vit C per 8 ounces, which is way less than wheat grass, which hits 30% at one full TBS. (that is why I only use 1 TSP wheat grass with my mix, which is plenty to give an energy boost and alter the flavor)
It's a trade off, a little Sugar or a little Vit C. I can't yet decide which one to stick with.