The best wine for making a bunch of sangria for a relatively low cost has got to be the Franzia wine in the box.
Hmm, premade sangria in a bottle? Interesting concept. Normally sangria is made with red wine, fresh fruit, a supplementary liquid such as club soda or lemon-lime soda, and a few shots of a spirit, such as brandy or gin. To get this premixed in a bottle, I'd say there are two ways to go or possibly a mix of the two.
You could use wine and all fruit juices to maintain a pulp free product.
Or, you could rack the wine onto the fresh fruit and let it do its thing, then rack off the sangria and leave behind the fruit trub(?).
A "White Sangria" would be nice as well. I make a quickie one for parties in the summer that is basically white wine, usually a Sauvignon Blanc, white grape juice, apple juice, orange juice, lime juice, and a few shots of brandy with plenty of ice in the pitcher (oh yeah, typically they are made by the pitcher).
Deliciously refreshing!