It's interesting what price points do to a bass:
$5-10K - Shen or some other high end chinese or Romanian; a carved La Scala or Wan Bernadel (also Chinese)
$10-20K - a "shop" German or Hungarian or Czech or Kolstein; Maybe a bass like mine (by Jorge Vasquez de Anda) that's a bit of an odd duck; or a Martin Sheridan, Paul Bryant or Jacques Gagnon
$20 - 40K - bottom end Italians? French, maybe; Poellmans; AND new basses by Hachez, Ross, Hannah Mayne, Cole, Schnitzler, Lloyd etc
$40-100K - Italian etc
The question that I think you've stumbled on actually was the question that won the Noble prize in Economics last year.
Example: you buy a bottle of wine for $5.99 (at least in LA you do) and you say "Wow, that's a great bottle of wine." The store says "oh boy, people think this is a great bottle of wine" and start charging $8.99 for it - and nobody buys it. At $8.99 you start thinking, "wow, for two bucks more I could get a REALLY good bottle of wine."
The economics become one of expectations - what do I EXPECT a $20K bass to do/sound like, etc? My hunch is that there are few $20/$30K basses out there that satisfy expectation two or three fold over a $10K bass (all things being equal), just as - to continue the analogy - you have to search high and low for a $30 bottle of wine that is 3x better than a ten dollar bottle - whereas - again, all things being equal - the $50 bottle of wine is immediately and significantly better.
I say (and again I have some limited experience) talk to modern luthiers, tell them what you want and have them make it for you - an dpocket the change.
Louis