I don't know where you can buy it in bulk, but DH and I made wine as favors for our wedding at a local winery. It ended up being around $4 a bottle. It was a lot of fun too.
DEFINITELY Trader Joes. They were great to work with. I think we only paid like $6/bottle and it tasted like a $10+ bottle. Plus you can return anything unopened. Go in and chat with them...their wine folks are great!
Re: cheap bulk wine