2. Labor: Just like we learned in our Econ 101 classes, labor is a big cost contributor. Someone needs to plant, care for, and pick the grapes. And then someone else needs to turn those grapes into wine and get them into bottles. Some cheaper wines are produced in more automated fashions that use harvesting machines, gyropalates, and robotic bottling/labeling lines.
5. Marketing: Some wineries are now part of mega-corporations like LVMH that believe wine should be advertised in every form of media possible and should be treated as a mass-marketed (and produced) product. No small boutique winery is going to want (or be able to afford) to buy up TV time or huge magazine ads. They look at their wine as an artistic expression, not a profit-driving commodity. All those catchy Korbel commercials aren't cheap and you can be sure that advertising cost was figured into the cost of your that bottle of Brut you're eyeing.
6. Prestige/Scores: Veuve Cliquot, Opus One, Petrus, Silver Oak...are they really worth it? Some say they are the best wines on the Earth and others think it is mostly hype (I vote for hype). A lot of time and effort (+1 Marketing) and money go into building up a reputation - these brands have done just that and they make sure to charge you for it. You can also bet that once a wine gets a high score from Parker, Spectator, or Tanzer it won't be a "value" for long.
Now, what you need to do is determine what factors are most important to you and buy your wine based on that. Do you think it is worth the extra few $$ to get a wine that is handmade or are you fine with mass-produced wines? Are you an organic food/wine devotee? Do you like wines that have pretty labels or fancy bottles that would make great mantle-pieces? Do you view wine as a status symbol and only want to be seen drinking the fanciest of wines? Once you figure out where your wine dollars are best spent, you will begin to get more out of your wine.