Boston has lots of options for inexpensive drinkable wines besides Costco and Trader Joe's, and Chowhounds know where the bargains are.
The Wine & Cheese Cask in Somerville is another great option, especially if it's running one of its quarterly sales. awkwardpause has tried a "very drinkable" Chilean Cabernet Sauvignon from here that was priced at about $10 a bottle.
Bin Ends [South Shore]
236 Wood Road, Braintree
The Wine & Cheese Cask [Somerville]
407 Washington Street, Somerville
Martignetti Liquors [Brighton]
1650 Soldiers Field Road, Brighton
1160 Boylston Street, Chestnut Hill
The Spirited Gourmet [Belmont]
448 Common Street, Belmont