Grapes, not juice
I saw a mention that a winery offered juice and sent an email. Turns out they offer grapes in lots as small as 50 pounds. The owner responded and was very informative and forthcoming. It's not as economical as buying 23 liter juice packs but the wine they sell goes for $25 per bottle. I doubt I could produce the same quality wine, but I could do it, per my calculations, for as little as $5 per bottle based on just juice, not considering other ancillary costs.
I'm seriously considering buying grapes, pressing and all the other stuff, in concert with a few friends that also make wine.
We'll see.