Many large liquor stores (including some grocery store liquor departments) have a "bargain bin" of wines that are half price. For some reason, these are often put in a bathtub. Anyway, a lot of these wines are plonk, but you can find some real bargains. Look especially for Chardonnays which are just past the three year mark, and California reds from regions not as well known as Napa or Sonoma.

Wines from Oregon and Washington are often very good value, especially Washington, since they're not as well known as California wines.

German wines tend to be good value too, if you like that style. Recent vintages have been rated very highly.

New Zealand wines are often excellent, if you like the unique tropical-fruit style of most of them

A few wineries are now putting good-quality wines in boxes, though most box wine is plonk. But if you can find one of the few good boxed wines, the equivalent cost per bottle can be amazingly cheap. In my experience the boxed wines last for weeks or months after opening with no loss of quality.