I often find people have a kind of placebo effect when it comes to expensive commodities. It's expensive so it has to be better. In the meantime, professionals buy generics: http://www.npr.org/sections/money/2014/07/25/334459041/when-...
That said, I can tell for a fact price often does not matter past a certain point -- it definitely isn't a good way to determine quality. I have had great bottles that sell for $15, and (not horrible but) not special ones that sell for $50 or $100. There are plenty of good $15 wines and plenty of bad ones. Same applies to the higher priced ones as well.
Often it's hit and miss, and you need to do your research! (Which isn't necessarily a bad thing)
Just don't buy a bottle based on how the bottle looks.
On the other hand, the average person is unlikely to be able to tell the difference between a $25 bottle of wine and a $2500 bottle of wine.
When you cook with wine you lose all the alcohol, which is the only constant between two bottles of wine. You're just left with the rest from which comes the taste.
There's no such thing as "cooking wine". Bad wine is bad wine. If you wouldn't drink it, don't cook with it.
That all being said, I personally think wine snobbery is basically bullshit and I think blind taste tests tend to support that view.
Still, a wine isn't bad because it's $5. Nor is it good because it's $30.
When I lived in the UK I'd often get by with the table wine from Tesco for under 5 pounds and honestly it was fine. I found quite a few decent bottles of Portugese and Chilean wine for under 10 pounds. Beaujolais wasn't more than 3-5 pounds.
This is a myth. Even after 2.5 hours of simmering/baking, 5% remains. Flambeing leaves 75%, and a 15 minute simmer still leaves nearly half.
You say that like its a bad thing.
Cooking with the wine is a great way for it to end up on the table surrounded by random glasses where "I don't want to trouble you", becomes "well, since its open anyway".
But if you are cooking with the wine, you already have the bottle open. Since an opened bottle of wine will rapidly deteriorate if you don't drink it within a fairly short time period (day or so), you may as well drink the remainder, thus put the open bottle on the table (where family/guests are gathered), and it will be consumed with relish.
Stuff like red wine sauces, whiskey glazed veggies, rum cakes, flambeed mushrooms, etc. that aren't cooked as long contain a very significant amount of alcohol.
The last wine I drank was a Montepulciano d'Abruzzo; I can't remember the specific winemaker, but it was quite nice and was less than $9, despite being bought in another European country.
I'm still in shock about wine prices in the US but SF in particular. ~18 months after I moved here. In Germany I could buy the same Californian wines for cheaper than here, not to speak of pretty good French, Italian, Spanish ones. It's less bad if you're outside of SF.
Apart from the fact than nobody should expect you to spend any money on anything... Just like everything else, wines differ, among others, in quality. If you spend 5 bucks on a bottle, chances are what you're drinking is really bad. It is possible to find decent wine in this range, but it's quite difficult.