Ascorbic acid is okay. You want to stay away from sorbates, sulphites or benzoates.
$7 for less than a gallon of juice is a bit much but you're paying for the organic qualities. However, I would probably get it because you can find a bung that fits that mouth and ferment right in there.
I used Trader Joe's spiced apple cider and though I cannot comment on how great it really worked due to me over-pitching my yeast, I do have some seemingly good cider. It was $2.99 for 2 quarts. Just to give you perspective. I think Trader Joe's had 2 quarts of organic apple juice for $3.99 but it was in a plastic bottle. Not that it matters, just kind of giving you an idea on their pricing versus what you're looking to buy here.