My wife and I have been picking up the heck out of that $4.99 / bottle from Costco. A Spanish Gernache/Syrah blend. I can't figure out how you make a bottle, cap it (not cork, so cheaper there), ship and store it to Costco (3-4 pallets per store) and then they sell it for $5 a bottle.
I suppose high crop loads, limited water, limited spray program. but even so there has to about $0.25 to $0.50/ bottle just in the bottle. with Tax and Import costs you are up to around $2.50-3.00 / bottle. The margins must be super, super thin. The cheapest I can make a bottle of wine for is around $2.50, with new bottle, cork, and no labor cost.
Oh and it's really pretty darn good wine for that price.
For the record we are at about 65-70% our own wines. We are down a bit from our max, since we "only" make about 30 gallons / year anymore, maybe even less.