lotus blossom,
I'm trying to do a little rough math here, which certainly isn't my strong suit!
If the Ocean Spray is 1/4 pure juice (rounding 27% to 25% for simplicity sake), then you're getting 16 ounces of pure juice for the $2.50 bottle of 64 ounce cocktail (64 ounces divided by 4 equals 16 ounces). This means 16 ounces of juice for $2.50 is about 15 or 16 cents per ounce ($2.50 divided by 16 ounces).
If the cost of the healthfood pure juice is anywhere in the ballpark of 15 to 16 cents per ounce (I personally would think that even 20 cents per ounce would be ok for me), then you're better off diluting it yourself. At any rate, even if the cost per ounce is even higher, you'll need to weigh the cost to your health of consuming so much sugar.
--Rheanna