All of the above. The wood, the tone, the quality of build, the design, the brand name, the "Made in USA" label...
Seriously, though, they cost that much, because everything of quality costs that much. For me, the price of a new StingRay is the entry level of professional quality instruments. The quality available from Music Man is simply a step above what most other companies are offering in that price range. I feel that same way about my Warwick, and you should see what Warwicks cost in the US these days...
The only other large brand name basses I'm considering these days besides more StingRays and more Warwicks are the Paul Reed Smith Gary Grainger models, and they're custom build only ($$$$$$$).