as i understand it - big scores aside - most pricing for variety is based on cost/ton. some growers even have minimum retail price parameters included in contracts.
Why would you think that price is based on cost? Is that true for anything else? That’s commodity pricing. Wine is a Veblen good. Cost has nothing to do with the price.
To respond to the OP - you’re looking at California. In France, the grape is not necessarily what drives cost. I believe that there’s more Merlot planted in Bordeaux than there is Cab. In some places it’s only a small percentage of the blend, in others it’s much of the blend. The reason people pay more for a grape in California has to do with history and marketing.
When the US industry was starting up again in the 1960s and even the 1970s, the US looked to France as the epitome of taste and class. Italy and Italian food and wine were pretty much disdained in most of the US. Pizza was just starting to become popular and there no Mario Batalis around.
There were always highly-regarded wines made in many parts of Europe but the Brits were next to France, they bought the stuff that as exported from there, and as they were the pre-eminent power in the world, they took those wines around with them. There’s a reason so many Bordeaux houses were and are owned by non-French people - the wine was always a creation of the marketers, not little romantic wine makers, and there was great money to be made in selling it. So it’s always been an attractive place to investors from around the world.
Especially after WWI and WWII, the producers in Spain and Portugal who had once been mainstays of the British wine trade were pretty much off the map, Germany, which produced the most expensive and revered wines, was a shamed and beaten opponent, and the Austro-Hungarian empire, which produced the wonderful sweet wines was no longer in existence. Italy produced a lot of peasant wine that nobody outside of the country cared for.
So French wine, particularly wine from Bordeaux, was considered the best and when the Americans looked for a standard, they looked to Bordeaux and France. Jefferson had written about Bordeaux, De Gaulle served it to Jackie Kennedy, and that was the wine to beat. What grapes were in the most prestigious? Why Cabernet Sauvignon. So the folks in California planted Cab Sauv and tried to make something like Bordeaux.
Remember that at the time there was probably more Carignan and Barbera and Charbono planted in CA than Cab. But all that stuff was all planted by old Italian peasant farmers or by big commercial outfits looking for high- producing varieties.
Mondavi and others taught Americans to buy by grape variety and certain varieties are considered “better” than others. Because of that, people will pay more for those wines. Look at notes on this forum - people have said that they prefer 100% Cab to any blend. There’s no reason on earth that a single variety can or should produce a better wine than a blend, but that’s not what people want to hear and if they’re willing to pay extra for a monovarietal, why not make it for them?
Napa can grow lots of things. I think it makes excellent Zinfandel for example. But if I were a grower and I could get five times as much per ton for Cab, I’d rip out the Zin and plant Cab. My cost might be the same, but my price wouldn’t be!