Whilst there are exceptions, thankfully most SV bottlings aren’t double the price of the standard Barolo: I reckon +25% would be the average. At that level I’d say it’s situational, not just in producer/SV, but also what we’re looking for.
i.e. SV’s can be useful when wanting something more specific e.g. one that might be approachable young, vs. one that will absolutely shine in the cellar. They often benefit as well from being selected into that bottling, with some non selected grapes
going into the std. barolo (or into the langhe nebbiolo, if say young vines or not ideal quality).
Std. Barolo, often blended across sites, can still be very good indeed, and some make a point of not making it a ‘lower quality’ wine than their SV bottlings, instead championing the old approach of trying to make such a blend ‘more than the sum of its parts’. Such wines might be especially good in a tricky vintage, able to soften issues across the blend, and indeed in some tricky vintages, a std. barolo might be all they make.
- Langhe nebbiolo often nominally the best value of all, but also perform a wonderful role on being ready to drink earlier / not closing down hard (if at all), and thus allowing us time to let the fancier wines sleep for the time they deserve to show well / excite. Definitely good ‘school night’ wines, but better examples can happily show well / shine with a sunday roast.
Sp at +20-25% of the standard bottling, I’d say it’s more of a preference thing, and if exploring the region, you’ve got options of how deep you want to delve into terroir nuances. In terms of detail, the progression is something like:
Barolo (potentially a blend across many communes)
Barolo del commune di… (e.g. Barolo del commune di Verduno, using grapes only from Verduno)
Barolo [single vineyard] (e.g. Barolo - Rocche dell’Annunziata, which is a cru within La Morra commune)
plus there are ‘riserva’ bottlings, often single vineyard, but not always. Typically they’ll have an extra year’s age before release vs. a non-riserva. How different they are depends on what the producer is doing when selecting from the grapes they have, and sometimes how they treat them in the barrel.
As for difference in quality between a wine and one double the price. I don’t see Barolo as much different to any other leading wine region:
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Avoid the very bottom, typically negociant labels or lesser co-ops, relying solely on the prestige of ‘Barolo’, with the wine in the bottle often an insipid wine offering less of interest than similarly priced Langhe nebbiolo
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Once out of this ‘commodity wine’, there’s super value to be had, but IMO better by getting to know lesser known producers, rather than bigger companies trying to hit a price point like Fontanafredda, Marchesi di Barolo etc.
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As you progress up in price, I’d say the value gets progressively worse (pretty much in line with your own thoughts), and that especially true of the wines that are talked up by critics, and also to a degree by us lot in a groupthink way. The best value IMO is found by sniffing it out yourself, as there’s not a horde of people following the same recommendations.
That said… It should never solely be about a focus on value, otherwise we’d all just be drinking riesling every day 
Having a choice of: a good representative, yet approachable Barolo; or a specific more floral cru; or a rugged tannic monster to have ageing in the cellar definitely helps gives us those choices we both love and get overstressed about. It’s also good to have ‘school night’ wines, weekend wines, and special meal wines, so a range of prices can be very sensible.
FWIW I think the most expensive Barolo I’ve bought was probably ~ €65, but if inflation adjusting, maybe make that €80. Rather frustratingly, though, some of those would now cost a lot more e.g. wines from Burlotto, Bartolo Mascarello, Giacomo Conterno Monfortino, Lorenzo Accomasso, Giuseppe Rinaldi (without an allocation of these wines, that often are much closer to more reasonable ex-cellar pricing). I try not to look at current market prices - it doesn’t help the drinking experience. Such bottles though are lovely to share at wine tastings or with friends.
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