If you know what you're looking for, it's often possible to find some good bargains by buying wine at auction. Winebid.com is the auction I use, mainly because they have a Chicago office where I can pick up wines in person if I wish.
Having just visited California wine country, I am amazed at the good buys in California wines in the current auction. Goldeneye Pinot Noir (from Duckhorn), for example, will cost you $55 in the shop, but the bid right now on a 2006 Goldeneye is only $30. And I suspect that will be the sale price since the wine escaped last week's auction without a bid. Anderson Valley winemakers recommend five to eight years' aging for their Pinots, so this wine is just approaching its drinking window. The bid on the 2006 Turnbull Cellars Cabernet is $20 (less than half the current release) and a terrific buy for an Oakville Cabernet.
French wines are ordinarily a bit less of a bargain, but I saw a 1998 Raymond Usseglio Chateauneuf for a bid of $25. That's less than I paid for this wine on release, and I'm expecting great things from it. The Hachette Guide considered it one of the best Chateauneufs of the vintage. Online reviews indicate that it's somewhat bretty at this stage, but some, including myself, consider that a plus in traditional Chateauneuf du Pape.
One way I have of finding bargains is by bottom fishing. On the home page, I select "other ways to browse." That gives every wine in the auction, and I hit the price button to browse from low to high. Most of the wines in the $5 and $10 category are low-end commercial wines plus other wines that could be a bit old to drink. But there are also some occasional bargains. Last month, I found two Anderson Valley Pinots (1998 Greenwood Ridge and 2000 Elke Vineyards) for $15 apiece. They may be over the hill, but I'm willing to take the chance in order to learn something about the ageworthiness of this appellation.
The negative is that buyers pay a 15% premium. Sales tax may or may not be charged, depending on the state. And there is a shipping cost that could add as much as $4 to $5 a bottle depending on how much is shipped at one time. Even so, it's possible to find some bargains.