Wine quality does not rise in a straight line with price. It rises steeply at the bottom, flattens through the middle, and at the top it stops tracking quality at all and starts tracking scarcity. Knowing roughly where those bends fall is the most useful commercial fact in wine.
Why the cheapest bottle is mostly not wine
A fixed cost sits under every bottle regardless of what is in it: the glass, the closure, the label, the carton, the shipping, the retailer's margin, and in many countries a flat excise duty that does not scale with price. Together these can account for most of the price of a cheap bottle.
The consequence is arithmetic rather than snobbery. If the fixed costs are, say, five units, then a six-unit bottle has one unit of wine in it and a twelve-unit bottle has seven. You did not double your money on wine; you multiplied it several times over. That is why the jump from the cheapest tier to roughly double it is the largest quality gain available anywhere on the shelf, and why the jump from thirty to sixty is barely noticeable by comparison.
Where value hides
Value concentrates wherever the name on the label is unfamiliar, because buyers will not pay for a word they cannot pronounce or place. Portugal is the clearest example: 250 native grape varieties, serious quality, and prices held down by the fact that almost nobody outside the country can name one of them.
The same applies to Greek assyrtiko and xinomavro, Hungarian dry furmint, Bulgarian mavrud, South African chenin blanc, Chilean país and cinsault, Loire cabernet franc, and German riesling, which has been the best value in fine white wine for thirty years because buyers assume it is sweet.
Conversely, you pay a premium for famous names, for regions that appear in films, and for grapes everyone already knows. A cheap Bordeaux, a cheap Burgundy or a cheap Champagne is usually worse than a good wine from a region with no reputation to sell.
What the top of the market is actually pricing
Above a certain point, price reflects scarcity, reputation, critic scores and auction demand rather than measurable quality. A grand cru vineyard may be two hectares in size, and no amount of money increases its output. That is a genuine reason for a high price, and it is not the same reason as the wine being proportionally better.
Blind tastings consistently show that trained tasters can distinguish quality tiers but not fine gradations at the top, and that untrained tasters barely track price at all. That is worth knowing before deciding what a bottle is worth to you.
Practical rules
Spend the extra step up at the bottom of the range. It buys more than any other increment.
Buy the unfamiliar region and the familiar grape, or the familiar region and the unfamiliar grape. Paying for both is where the premium sits.
In a restaurant, avoid the second cheapest bottle. It is the one most often chosen by people who do not want to seem cheap, which is exactly why it tends to carry the highest markup on the list.
Buy six of something you liked rather than six different things you might. Most people learn more from drinking one wine repeatedly than from a scattered survey.